NERVOUS SYSTEM

Cells of the Nervous System

Neurons
Functions (CRIME) ▪ Also called nerve cells
1. Controlling muscles and glands. ▪ Receive stimuli, conduct action potentials,
2. Receiving sensory input. transmit signals
3. Integrating information. Cell body – contains a single nucleus; source of information for
4. Maintaining homeostasis. gene expression n
5. Establishing and maintaining mental activity.
Dendrites – extensions of the cell body; receive information
Divisions of the Nervous System from other neurons; transmit the info toward the neuron cell
I. Central Nervous System body
▪ Brain and spinal cord
Axon – single long cell process; conduct action potentials
from one part of the brain or spinal cord to another part
II. Peripheral Nervous System
➢ Axon of sensory neurons – conduct action potentials
▪ Nerves and ganglia towards the CNS
a. Sensory Division – afferent (toward) ➢ Axon of motor neurons – conduct action potentials
division; conducts action potentials from away from the CNS
sensory receptors to the CNS
• Sensory neurons – neurons that Axon hillock – where the axon leaves the neuron cell body
transmit action potentials from
the periphery to the CNS Nissl bodies – rough ER found in the cell body of a neuron

i. Somatic Sensory Fibers – carry info Schwann cells – form a myelin sheath (increases speed of
from stimuli coming from the skin, impulse transmission)
skeletal, muscles,joints
Collateral axons – branches of axons
ii. Visceral Sensory Fibers – transmits
impulses coming from the visceral Types of Neurons
organs 1. Multipolar neurons – many dendrites + a single axon
b. Motor Division – efferent (away) division; 2. Bipolar neurons – two processes: 1 dendrite + 1 axon
conducts action potentials from the CNS to
effector organs 3. Pseudo-unipolar neurons – single process that
• Motor neurons – neurons that divides into 2 processes: extends to the periphery +
transmit action potentials from extends to the CNS
the CNS toward the periphery
Neuroglia
i. Somatic Motor Nervous System /
▪ Non-neuronal cells of the CNS + PNS
Voluntary – transmits action
potentials form the CNS to the ▪ More numerous than neurons
skeletal muscles ▪ Retain the ability to divide

ii. Autonomic Motor Nervous 1. Astrocytes – major supporting cells in the CNS;
System / Involuntary – transmits stimulate/inhibit the signaling activity of nearby neurons;
action potentials from the CNS to help limit damage to neural tissue
cardiac, smooth muscles and ❖ Blood brain barrier – protects neurons from toxic
glands substances in the blood; allows exchange of
1. Sympathetic – figth-or- waster products + nutrients
flight system
2. Parasympathetic – 2. Ependymal cells – produce cerebrospinal fluid; help
resting and digesting move the cerebrospinal fluid through the CNS
system
3. Microglia – act as immune cells of the CNS’ protect the
iii. Enteric Nervous System – unique brain by removing bacteria and cell debris
subdivision; both sensory and
motor neurons contained within
the digestive tract
 4 – 5. Oligodendrocytes (CNS) and Schwann cells (PNS) Electrical Signals and Neural Pathways
– provide an insulating material that surrounds axons Resting Membrane Potential
Polarized cell membrane – uneven distribution of charge
Neural Signaling
▪ Communication among neurons Resting membrane potential – uneven charge
distribution in an unstimulated/resting cell; polarized
1. Reception – stimuli received by visual receptors in the ➢ Higher concentration of K+ inside CM
eye ➢ Higher concentration of Na+ outside CM
➢ Greater permeability of CM to K+ than to Na+
2. Transmission – sensory neurons transmit info to CNS
Leak channels – always open
3. Integration – info given is interpreted and an
appropriate response is determined Gated channels – closed until opened by specific signals

4. Transmission – the CNS transmits info to motor Chemically gated channels – opened by
neurons neurotransmitters

5. Actual response – muscle/glands receive infoand Voltage gated channels – opened by a change in membrane
instruction from motor neurons potential

Myelin Sheaths Sodium potassium pump – required to maintain the greater

▪ Highly specialized insulating layer of cells concentration of Na+ outside the CM and K+ inside

Unmyelinated axons – action potentials are conductedslowly Action Potentials

bcos in travels along the entire axon Excitable cells – RMP changes in response to stimuli that
activate gated ion channels
Myelinating axons – action potentials are conducted rapidly by
salutatory conduction Local current – Na+ diffuses quickly into cell

Nodes of Ranvier – gaps in the myelin sheath; where ion Depolarization – a change that causes the inside of the CM to
movement can occur become positive

Organization of Nervous Tissue Local potential – result of depolarization

Gray Matter – groups of neuron cell bodies + their dendrites;
very little myelin Threshold value – attainable local potential (critical pt.)
➢ In the CNS;
Action potential – constitution of depolarization and
❖ Cortex – GM on the surface of the brain
repolarization
❖ Nuclei – GM located deeper within the brain
➢ In the PNS; Hyperpolarization – the charge on the CM briefly becomes
❖ Ganglion – a cluster of neuron cell bodies more negative than the RMP
White Matter – bundles of parallel axons + myelin sheaths All-or-none fashion – threshold is reached = action potential
➢ In the CNS occurs; if the threshold is not reached = action potential
❖ Nerve tracts – conduction pathways; doesn’t occur
propagate action potentials from one area of
the CNS to another Continuous conduction – the action potential is conducted
➢ In the PNS; along the entire axon CM
❖ Nerves – bundles of axons + connective
tissue sheaths Saltatory conduction – action potentials jump from one node
of Ranbier to the next

The Synapse
Synapse – a junction where the axon of one neuron interacts
with another

Presynaptic terminal – end of the axon

Postsynaptic membrane – membrane of the dendrite or

effector cell

Synaptic cleft – space separating the presynaptic &

postsynaptic membrane
Neurotransmitters – chemical messengers

Synaptic vesicles – where neurotransmitters are stored

Hyperpolarized – the inside of the postsynaptic cell tends to

become more negative

Substance Effect Clinical Example

Acetylcholine Excitatory or Alzheimer disease
inhibitory
Norepinephrine Excitatory Cocaine and
amphetamines
Serotonin Generally Mood, anxiety, and
inhibitory sleep induction
Dopamine Excitatory or Parkinson disease
inhibitory
Gamma- Inhibitory Treatment of
aminobutyric epilepsy
acid
Glycine Inhibitory Poison strychnine
Endorphins Inhibitory Opiates morphine
and heroin

Reflexes
Reflex – an involuntary reaction in response to a stimulus
applied to the periphery and transmitted to the CNS

Reflex arc – neuronal pathway by which a reflex occurs

➢ Sensory receptor
➢ Sensory neuron
➢ Interneurons
➢ Motor neuron
➢ Effector organ (muscle or glands)

Neuronal Pathways
Converging pathway – two or more neurons synapse with the
same neuron

Diverging pathway – the axon from one neuron divides and

synapses with more than one other neuron

Summation – allows integration of multiple sub threshold local

potentials; brings the membrane potential to threshold and
trigger an action potential

Spatial summation – local potentials originate from diff.

locations on the postsynaptic neuron

Temporal summation – local potentials overlap in time

 Spinothalamic tract – transmits pain, light touch, and deep
SPINAL CORD pressure
▪ Extends from the foramen magnum to the 2nd Dorsal column – transmission of proprioception, touch, deep
lumbar vertebra pressure, vibration
▪ Provides a two-way conduction pathway to andfrom
the brain Spinocerebellar tracts – proprioception to cerebellum
Cauda equina – inferior end of the SC; spinal nerves exiting
there resemble a horse’s tail Descending Tracts
▪ Pathways that carry impulses from the brain to the
2 Main Functions periphery
1. Transmits info to and from the brain. Lateral corticospinal – muscle tone and skilled
2. Controls many reflex activities of the body. movements (hand)
White Matter of the SC Anterior corticospinal – muscle tone and movement of trunk
1. Dorsal (posterior) muscles
2. Ventral (anterior)
3. Lateral Columns Rubrospinal – movement coordination
a. Ascending tracts – conduct action
potentials toward the brain Reticulospinal – posture adjustment
b. Descending tracts – conduct action
potentials away from the brain Vestibulospinal – posture & balance

Gray Matter of the SC (shaped like the letter H) Tectospinal – movement in response to visual reflexes
1. Posterior horns
2. Anterior horns Cranial Nerves
3. Small lateral horns ▪ Transmit info to the brain form the sensory
receptors
Central canal – fluid filled space in the center of the cord ▪ 12 pairs

Ventral root – formed by ventral rootlets; Name Specific Function

I. Olfactory S S: smell
Dorsal root – formed by dorsal rootlets II. Optic S S: vision
M: 4-6 extrinsic eye
Dorsal root ganglion – ganglion in a dorsal root III. Oculomotor M muscles; P: constricts
pupils
Relfex Action IV. Trochlear M M: 1 extrinsic eye muscle
▪ Predictable, automatic response to a specific S: face + teeth; M: muscles
stimulus V. Trigeminal B
of mastification
VI. Abducens M M: 1 extrinsic eye muscle
1. Reception of the stimulus. S: taste; M: facial muscles;
2. Transmission of info to the CNS. VII. Facial B
P: salivary + tear glands
3. Integration (interpretation and determination of an Acoustic /
appropriate response).
VIII. Vestibulococh- S S: hearing + balance
4. Transmission of info from the CNS to a muscle.
lear
5. Actual response.
S: taste + touch to back of
Glossopharyng
Spinal Cord Reflexes IX. B tongue; M: pharyngeal
-eal muscles; P: salivary glands
Knee-Jerk Reflex
Stretch flex – simplest reflex; muscles contract in response to S: pharynx, larynx, viscera;
a stretching force applied to them X. Vagus B M: palate, pharynx, larynx; P:
viscera of thorax + abdomen
Knee-jerk reflex – patellar reflex; used to determine if the
higher CNS centers that normally influence this reflex are M: 2 neck + upper back
functional XI. Accessory M
muscles
XII. Hypoglossal M M: tongue muscles
Withdrawal Reflex
Withdrawal Reflex – flexor reflex; to remove a limb from a
painful stimulus Spinal Nerves
▪ Arise along the spinal cord; contains mixed nerves
Ascending Tracts ▪ 31 pairs
▪ Pathways that carry impulses form the ❖ 8 Cervical
periphery to various parts of the brain ❖ 12 Thoracic
❖ 5 Lumbar
 ❖ 5 Sacral Autonomic Nervous System
❖ 1 Coccygeal ▪ Preganglionic neuron
▪ Postganglionic neuron
Mixed nerves – contains both sensory and somatic motor ▪ Maintain internal homeostasis
neurons
Autonomic ganglia – where preganglionic neurons synapse
Plexuses – where nerves come together and thenseparate with postganglionic neurons
➢ Cervical plexus
➢ Brachial plexus I. Sympathetic ANS
➢ Lumbosacral plexus ▪ ‘Fight-or-flight’
▪ Prepares the body for action
Cervical Plexus ▪ Most active during stressful situations
▪ Originates from spinal nerves C1 to C4 ▪ Norepinephrine (main neurotransmitter)
Phrenic nerve – most important branc of the CP; innervates II. Parasympathetic ANS
the diaphragm (responsible for our ability to breathe)
▪ Activities result in conserving and restoring energy
Brachial Plexus ▪ Helps return the body to resting conditions
▪ Originates from the spinal nerves C5 to T1 ▪ Active during periods of calm and rest
▪ PS fibers are in the vagus nerve
1. Axillary nerve – innervates 2 shoulder muscles
+ the skin over part of it Autonomic Neurotransmitters
Acetylcholine – neurotransmitters of the
2. Median nerve – innervates the anterior forearm and parasympathetic division
intrinsic muscles
Norepinephrine – postganglionic neurons of the sympathetic
division
3. Radial nerve – innervates all the muscles in the
posterior arm and forearm + skin over the posterior
surface of the arm, forearm, hand Functions of the Autonomic Nervous System
Sympathetic Division
4. Musculocutaneous nerve – innervates the anterior ▪ Prepares a person for action by increasing HR, BP,
respiration, release of glucose
muscles of the arm + skin over the radial surface of
the forearm
Parasympathetic Division
5. Ulnar nerve – innervates most of the anterior forearm ▪ Involuntary activities at rest: digestion of food,
muscles and some of the intrinsic hand muscles + defecation, urination
skin over the radial side of the hand
Enteric Nervous System
Lumbosacral Plexus ▪ Consists of plexus within the wall of the digestive
▪ Originates from spinal nerves L1 to S4 tract

1. Obturator nerve – innervates the muscles of the 1. Sensory neurons – connect the digestive tract to the
medial thigh + skin over it CNS
2. Sympathetic & parasympathetic neurons –
2. Femoral nerve – innervates the anterior thigh muscles connect the CNS to the digestive tract
+ skin over it & medial side of the leg 3. Enteric neurons – located entirely within enteric plexus
❖ Capable of monitoring and controlling the
3. Tibial nerve – innervates the posterior thigh muscles, digestive tract independently of the CNS
the anterior & posterior leg muscles, most of the
intrinsic foot muscles + skin over the sole of the foot

4. Common fibular nerve – innervates the muscles of the

lateral thigh & leg, some intrinsic foot muscles + skin
over the anterior & lateral leg, dorsal surface of the
foot

Sciatic nerve – CT sheath that bounds the tibial and common

fibular nerve
 Epithalamus
BRAIN
2.
▪ Smallest area superior + posterior to the thalamus
▪ Soft, wrinkled mass of tissue that is highly complex ▪ Consists of few small nuclei (emotional and visceral
and adaptive; 3 pounds response to odors) + pineal gland
▪ 25 billion neurons
Pineal gland – an endocrine gland that may influence the
▪ Requires a continuous supply of oxygen and glucose onset of puberty; role in controlling some long term cycles
I. Brainstem 3. Hypothalamus
▪ Connects the spinal cord to the remainder of the brain ▪ Most inferior part
▪ Controls the heart rate, blood pressure, and
▪ Consists of several small nuclei; maintaining
breathing homeostasis
▪ Damage can cause death ▪ Control of body temp., hunger, and thirst
▪ Sensations such as sexual pleasure, rage, fear, and
1. Medulla Oblongata relaxation
▪ Most inferior portion of the brainstem
▪ Important reflex actions like vomiting, sneezing, Important Homeostatic Mechanisms
coughing, swallowing 1. Control center of the ANS.
▪ Gray matter consists of various nuclei that serve as 2. The link bet. the nervous and endocrine systems.
vital centers 3. Helps maintain fluid balance.
❖ Cardiac centers – control HR ❖ Anti-diuretic hormone (ADH) –
❖ Vasomotor centers – regulates BP bu regulates water excretion by the kidneys
controlling blood vessel diameter 4. Regulates body temperature.
❖ Respiratory centers – initiates and 5. Regulates food intake (appetite and satiety centers).
regulates breathing 6. Regulates sleep-wake cycles.
▪ Pyramids – two prominent enalargements 7. Influences sexual behavior and emotional
aspects of sensory input.
2. Pons (bridge)
▪ Relay information bet. the cerebrum and the Infundibulum – controlling the secretion of hormones from the
cerebellum pituitary gland
▪ Resembles an arched footbridge
▪ Regulates respiration, swallowing, sleep Mammillary bodies – involved in emotional responses to odors
and in memory
3. Midbrain
III. Cerebellum
▪ Smallest region of the brainstem
▪ Second largest part of the brain; 2 hemispheres
▪ 4 mounds called the colliculi
❖ 2 inferior; major relay centers for the ▪ Responsible for coordination of movements
auditory nerve pathways in the CNS ▪ Comparator – a sensing device that compares data
❖ 2 superior; visual reflexes and receive touch from two sources
and auditory input ▪ Proprioceptive neurons – innervate joints, tendons,
muscles; provide info about the position of body
4. Reticular Formation parts
▪ A group of nuclei scattered throughout the brainstem 1. Helps in smooth and coordinated body
▪ Regulating cyclical motor functions; respiration, movements (comparator function).
walking, chewing 2. Maintains muscle tone posture.
▪ Damage can result in coma 3. Maintain balance and equilibrium
▪ Reticular activating system – plays an important role 4. Important in learning motor skills.
in arousing and maintaining consciousness
IV. Cerebrum
II. Diencephalon
▪ Largest and most prominent part of the brain
▪ Part bet. the brainstem and the cerebrum
1. Sensory Function – receives info from sensory
1. Thalamus receptors and interprets it
▪ Largest part of the diencephalon 2. Motor Function – responsible for all voluntary
▪ Major relay center for all sensory info (except movement and some involuntary ones
smell) to the cerebrum; plays a gating rol 3. Association Function – responsible for all of the
▪ Influences mood and registers an uncomfortable intellectual activities of brain
perception of pain
▪ Interthalamic adhesion – connects the two large,
lateral parts of the thalamus
4 Lobes Right and Left Hemispheres
1. Frontal Lobe Right hemisphere – three dimensional or spatial perception,
▪ Control of voluntary motor functions, motivation, musical ability
aggression, mood, olfactory reception
▪ Primary motor area: consciously move our skeletal Left Hemisphere – analytical hemisphere; mathematics and
muscles speech
▪ Broca’s area – speech center
▪ Prefrontal area – reposible for executive functions Memory
Working memory – stores info required for the immediate
performance of a task; 7 digit phone no.
2. Parietal Lobe
▪ General Sensory Area – receives info from the Short-term memory – last longer; can be retained for a few
sensory receptors in the skin and joints mins. to a few days
▪ Wernicke’s area – sensory speech area
Long-term memory – stored for only a few minutes or become
3. Occipital Lobe permanent by consolidation
▪ Receiving and perceiving visual input
▪ Primary visual area – receives visual info Consolidation – a gradual process involving the formation of
new and stronger synaptic connections
▪ Visual association area – portion where visual info
is integrated
Declarative memory – explicit memory; retains facts and
related emotional undertones
4. Temporal Lobe
▪ Primary auditory area – center for reception of Procedural memory – reflexive memory; development of
auditory messages motor skills
▪ Auditory association area – where auditory
messages are integrated Memory engrams – memory traces; long-term retention of a
▪ Psychic cortex – abstract thoughts and thought/idea
judgments
Limbic System
Gyri – folds and convolutions; increase the surface area of the ▪ A group of interconnected nuclei involved in
cortex and intervening grooves (sulci)
memory and regulation of emotion
Sulci – shallow grooves
Hippocampus – formation and retrieval of memories
Fissures – deep groves Amygdala – filter sensory info and evaluates it in terms of
emotional needs
Longitudinal fissure – divides the cerebrum into left and right
hemispheres Meninges, Ventricles, and Cerebrospinal Fluid
Meninges
Cerebral cortex – outermost layer of the cerebrum; consists of
gray matter ▪ Surround and protect the brain and spinal cord

Corpus callosum – connects the right and left hemispheres 1. Dura mater – most superficial and thickest meninges
❖ Epidural space – bet. the dura mater & the
Central sulcus – separates the frontal and parietal lobes vertebrae
❖ Epidural anesthesia – clinically important as
Lateral fissure – separates the temporal love from the rest the injection site of spinal nerves; given to
women during childbirth
Insula – fifth lobe; deep within the fissure
2. Arachnoid mater – thin, wispy, 2nd meningeal
Basal Nuclei membrane
❖ Subdural space – space bet. the dura mater
▪ Group of functionally related nuclei and the arachnoid mater; contains small amt.
of serous fluid
Corpus striatum – located deep within the cerebrum ❖ Spinal block – to inject anesthetic into the
area
Substantia nigra – darkly pigmented cells in the midbrain
❖ Spinal tap – to take a sample of CSF

3. Pia mater – 3rd meningeal membrane; very tightly

bound to the surface of the brain and spinal cord;
filled with CSF and contains blood vessels
 ❖ Subarachnoid space – bet. the Aphasia – absent/defective speech/language
arachnoid and pia matter comprehension

Ventricles Brain Waves and Consciousness

▪ Fluid filled cavities Electroencephalogram (EEG) -

Lateral ventricle – relatively large cavity in each cerebral Brain waves – wave like patterns
hemisphere
Alpha waves – awake but in a quiet, resting state with eyes
Third ventricle – a smaller, midline cavity close

Fourth ventricle – located at the base of the cerebellum Beta waves – occur during intense mental activity

Cerebral aqueduct – a narrow canal that connects the 3rd and Delta waves – occur during deep sleep in infants and in patients
4th ventricle
Theta waves – observed in children; also in adults who are
Cerebrospinal fluid frustrated or have brain disorders
▪ Provides a protective cushion around the CNS
Effects of Aging on the Nervous System
Choroid plexus – produces CSF; specialized structures made of ▪ Motor functions decline
ependymal cells ▪ Mental functions (memory) decline
Arachnoid villi – structures that project from the arachnoid
layer; where blood is reabsorbed

Hydrocephalus – accumulation of CSF in the ventricles

Motor Functions
Involuntary movements – occur without a conscious thought

Voluntary movements – consciously activated to achieve a

specific goal; walking, typing

Upper motor neurons – have cell bodies in the cerebral cortex

Lower motor neurons – have cell bodies in the anterior horn

Motor Areas of the Cerebral Cortex

Primary motor cortex – control voluntary movements of
skeletal muscles

Premotor area – where motor functions are organized before

they are actually initiated in the primary motor cortex

Pre-frontal area – where planning and initiating movements

occur

Other Brain Functions

Communication bet. the Right & Left Hemispheres
Commissures – connection bet. the two hemispheres

Corpus callosum – largest commissure

Speech
Sensory speech area – Wernicke area; a portion of the
parietal lobe

Motor speech area – Broca area; inferior portion of the

frontal lobe