central nervous system, spinal nerves, and cranial nerves physiology... · central nervous system,...

Copyright 2010, John Wiley & Sons, Inc.

Chapter 10

Central Nervous

System, Spinal

Nerves, and Cranial

Nerves


End of Chapter 10

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Spinal Cord Structure: Protection and

Coverings

Vertebrae

Spinal meninges

Three layers of connective tissue

Dura mater

Arachnoid mater

Pia mater

Continuous with cranial meninges

Cerebrospinal fluid (CSF)


Spinal Meninges and Spaces

Epidural space: between vertebrae and dura mater

Dura mater- tough ,dense connective tissue Extends to vertebra S2 (well beyond spinal cord)

Arachnoid mater: resembles spider’s web Extends into subarachnoid space

Subarachnoid space CSF circulates in this space

Pia mater: thin, delicate layer Adheres to surface spinal cord (and brain)

Contains blood vessels


Spinal

Meninges

and Spaces


Gross Anatomy of Spinal Cord

Extends from medulla of brain to L2 vertebra

Cauda equina (horse’s tail)

Extends inferior to end of spinal cord

Consists of roots of lumbar, sacral and coccygeal spinal nerves

Left and right halves partially separated by

Anterior median fissure and posterior median sulcus

Small central canal (filled with CSF) in middle

Enlargements: cervical and lumbar regions

Points of origins of nerves to upper and lower limbs


Gross

Anatomy of

Spinal Cord


Internal Structure of Spinal Cord

Gray matter forms “H” (or “butterfly”)

Three horns on each side; sites of cell bodies Posterior gray horns: contain sensory neurons

Anterior gray horns: contain somatic motor neurons

Lateral: contain autonomic motor neurons

White matter (surrounds gray “H”)

Consists of white columns Posterior, anterior, and lateral columns

Contain tracts (bundles of axons)

Sensory tracts: ascending to brain

Motor tracts: descending from brain


Internal Structure of Spinal Cord


Spinal Nerves 31 pairs

Named according to level of vertebra

C1-C8, T1-T12, L1-L5, S1-S5, 1 coccygeal

Emerge from spinal cord through intervertebral

foramina

Nerves attached to spinal cord by 2 roots

Dorsal root: made of axons of sensory neurons

Dorsal root ganglion: swelling containing cell bodies of

sensory neurons

Ventral root: composed of axons of motor neurons

Both somatic motor and autonomic motor


Spinal Nerve Composition

Formed by 2 spinal nerve roots

Are mixed:

Formed from dorsal root (sensory) and ventral

root (motor) root

Connective tissue coverings

Individual axons wrapped in endoneurium

Axons grouped in fascicles wrapped in

perineurium

Outer covering = epineurium


Spinal Nerve Composition


Distribution of Spinal Nerves

Spinal nerves branch after pass through

intervertebral foramina

Some join with branches from neighboring

nerves to form plexuses

Nerve names relate to region innervated

Spinal nerves T2-T12 do not form plexuses

Called intercostal nerves

Supply abdominal muscles, skin of chest and

back, and muscles between ribs.


Plexuses

Cervical plexus

Supplies posterior head, neck, shoulders, and diaphragm

Important nerves: phrenic to diaphragm

Brachial plexus

Supplies upper limbs + some neck and shoulder muscles

Important nerves: radial, ulnar, axial, median to arm, forearm, hand


Plexuses

Lumbar plexus

Supplies abdominal wall, external genitalia, and

part of lower limbs

Important nerves: femoral (to anterior thigh:

quads)

Sacral plexus

Supplies buttocks, perineum, and most of lower

limbs

Important nerves: gluteal, sciatic (to posterior

thigh and all of leg and foot)


Spinal

Cord


Spinal Cord Functions

Pathways for nerve impulses within tracts

Ascending (sensory). Example: spinothalamic

Descending (motor). Example: corticospinal

Reflexes: fast, involuntary sequences of

actions in response to stimuli

Can be simple (withdrawal) or complex (learned

sequence such as driving car)

Levels

Spinal (reflex arc): simple

Cranial: more complex


Reflex Arc

1. Sensory receptor: responds to stimulus

2. Sensory neuron: through dorsal root

ganglion and root posterior horn

3. Integrating center: single synapse

between sensory and motor neurons

4. Motor neuron: from anterior horn

ventral root spinal nerve

5. Effector: muscle responds


Example of Reflex Arc: Patellar Reflex

1. Sensory receptor is stimulated by tap on

patellar tendon

2. Sensory neuron: through dorsal root

spinal cord

3. Integrating center: single synapse in

spinal cord

4. Motor neuron: through ventral root

spinal nerve femoral nerve

5. Effector: quads contract, extend leg


Example of Reflex Arc: Patellar Reflex


Brain: Major Parts

Brain stem: continuous with spinal cord Medulla oblongata, pons, midbrain

Diencephalon: superior to brain stem Thalamus, hypothalamus, and pineal gland

Cerebrum: largest part and most superior Surface covered with gray matter: cortex

Deep to cortex is cerebral white matter

Cerebellum: posterior and inferior Means “little brain”

Cranial meninges: dura mater, arachnoid mater, and pia mater


Brain: Major Parts


Brain Blood Supply and Blood-Brain

Barrier

Requires 20% of the body’s O2 supply

4 min lack permanent damage

Requires continuous glucose supply

Protected by blood-brain barrier

Allows passage of lipid soluble materials: O2,

CO2, alcohol, anesthetic agents

But controls entry of most harmful materials

Created by tight capillaries and astrocytes


Cerebrospinal Fluid (CSF)

Formed in the 4 ventricles of brain Lateral (#1 and 2) 3rd 4th ventricle

Formed in choroid plexuses By filtration and secretion of blood plasma

In specialized capillary networks (covered by ependymal cells) in walls of ventricles

Pathway Through 4 ventricles central canal of spinal cord

and within subarachnoid space

Reabsorbed through arachnoid villi into blood in superior sagittal sinus

Cushions brain and provides nutrients


Cerebrospinal

Fluid (CSF)


Brain Stem: Medulla Oblongata

Most inferior part of brainstem White matter connects spinal cord and other parts

of brain

Contains vital nuclei Cardiovascular center

Regulates heart rate, blood pressure

Medullary rhythmicity area Adjusts respiratory rhythm

Other sensory and reflex motor areas

Cranial nerves VIII-XII attached here


Brain Stem: Pons

Serves as a “bridge”

Connects medulla to midbrain and above

Contains ascending and descending tracts

Connects left and right sides of cerebellum

Contains nuclei

Motor relays from cerebrum to cerebellum

Helps control breathing

Cranial nerves V-VIII attached here


Brain

Stem


Brain Stem: Midbrain

Connects pons to diencephalon

Large tracts: cerebral peduncles

Nuclei:

Substantia nigra: related to Parkinson disease

Red nuclei: help coordinate movements

Origin of cranial nerves III and IV (control eye movements)

Superior colliculi: nuclei involved in Scanning eye movements

Responses to visual stimuli

Inferior colliculi: responses to auditory input


Reticular Formation

Netlike arrangement of gray and white matter

Contains ascending and descending tracts

Ascending part = reticular activating system

(RAS)

Carries sensory pathways to cerebral cortex

Helps maintain consciousness

Helps induce sleep


Reticular Formation


Diencephalon Thalamus: major sensory relay center

Also motor, autonomic, and consciousness functions

Hypothalamus: lies inferior to thalamus Control of pituitary and hormone production

Works with ANS regulating many viscera

Involved with feelings and behavior patterns

Regulation of eating, drinking, fluid levels

Control of body temperature

Regulation of circadian rhythms, sleep, waking

Pineal gland: secretes melatonin Controls sleep, biological clock


Diencephalon


Cerebellum

Location: posterior to medulla and pons,

inferior to cerebrum

Attached to brain stem by cerebellar peduncles

Structure:

Two cerebellar hemispheres

Cerebellar cortex: gray matter

Tree-like appearance (seen in sagittal section) of

white matter and gray nuclei


Cerebellum

Functions

Receives wide range of sensory input from

muscles, joints, tendons, eyes, inner ears

Compares actual movements with intended ones

Helps produce smooth, coordinated movements

Helps execute skilled motor activities

Regulates posture and balance


Cerebrum: Structure

Cerebral cortex

Internal white mater

Deep gray nuclei

Surface folds of cerebral cortex: gyri

Grooves between gyri: sulci

Longitudinal fissure: divides cerebrum into left and right hemispheres

Hemispheres connected by corpus collosum


Cerebrum: Structure

Each hemisphere has 4 lobes

Frontal, parietal, temporal, occipital

Central sulcus separates frontal, parietal

Precentral gyrus anterior to sulcus: primary motor

area

Postcentral gyrus: primary somatosensory area

Deep gray nuclei: basal ganglia

Globus pallidus, putamen, caudate nucleus


Cerebrum


Limbic System

Ring of structures on inner border of

cerebrum and floor of diencephalon

Called “emotional brain”: plays primary role in

pain, pleasure, anger, affection and in

behavior

Involuntary activity related to survival

Important in memory development


Limbic System


Functional Areas of Cerebral Cortex

Specialized areas in specific regions of cerebral cortex

Sensory areas receive input perception

Motor areas initiate movements

Associative areas complex integration: memory, emotion, reasoning, judgment


Sensory Areas

Primary somatosensory area: postcentral gyrus Input includes: touch, proprioception, pain, itching, tickle,

temperature

Primary visual area: occipital lobe

Primary auditory area: temporal lobe

Primary gustatory (taste) area: base of postcentral gyrus

Primary olfactory (smell) area: medial aspect of temporal lobe


Motor Areas

Located anterior to central sulcus

Primary motor area: precentral gyrus

Broca’s speech area

Interacts with premotor area and primary motor

area to regulate breathing and speech muscles

Is in left hemisphere in 97% of persons


Association Areas

Adjacent to sensory and motor areas and connected via association tracts

Integrate and interpret information

Examples Somatosensory association area

Posterior to primary somatosensory area

Integrates sensation: exact shape and texture of object compared with stored memories

Wernike’s area: left temporal, parietal lobes Interprets meaning of speech: words thoughts

Right hemisphere adds emotional content


Cerebrum: Functional Areas


Somatic Sensory Pathways

Relay sensory information from periphery to

cerebral cortex

3 neurons in each pathway

Cell body #1 in dorsal root ganglion

Cell body #2 in spinal cord or brain stem

Cell body #3 in thalamus; axon extends to

cerebral cortex (somatosensory area in

postcentral gyrus)

Most sensory input to right side of body

reaches left side of brain (and vice versa)


Somatic Sensory Pathways

Posterior column - medial lemniscus pathway

senses

Fine touch: body location, texture, size

Proprioception: position and motion of body parts

Vibrations: fluctuating touch stimuli

Spinothalamic pathways

Anterior and lateral spinothalamic tracts

Relay impulses for pain, tickle, itch, hot, and cold

sensations


Somatic

Sensory

Pathways


Somatic Motor Pathways

Signals come from

Upper motor neurons: via corticospinal tracts

Basal ganglia: help with muscle tone

Cerebellum: coordination

Sensory neurons or interneurons via reflexes

Impulses activate lower motor neurons

Cell bodies in anterior gray of spinal cord

Axons ventral root spinal nerve muscle

voluntary movements


Somatic Motor

Pathways


Somatic Sensory and Motor Pathways Interactions Animation

Somatic Sensory and Motor Pathways

You must be connected to the internet to run this animation.

http://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_somatic_path/anim_somatic_path/screen0.swf


Lateralization

Brain controls opposite side of the body: all sensory and motor pathways cross in CNS

Left side of the brain controls right side of body

Right side of brain controls left side of body

Left hemisphere important for spoken and written language, numerical and scientific skills, and reasoning

Right side more involved with spatial and pattern recognition and emotional content


Memory

Process for storing and retrieving information

Involves structural and functional changes

Involves association areas, parts of limbic system, and diencephalon

Skill memory also involves cerebellum and basal ganglia


Cranial Nerves (Table 10.2)

I. Olfactory: special sensory—smell

II. Optic: special sensory—vision

III. Oculomotor: motor—control of eye movements

IV. Trochlear: motor—control of eye movements

V. Trigeminal: mixed

General sensory: touch, pain, pressure, hot, cold in face

Motor: to muscles used for chewing


Cranial Nerves

VI. Abducens: motor—control of eye movements

VII.Facial: mixed

Special sensory (taste) from anterior of tongue

Motor to muscles of facial expression, tear glands, and some salivary glands

VIII.Vestibulocochlear: special sensory—ear


Cranial Nerves

IX. Glossopharyngeal: mixed

Sensory for posterior of tongue, pharynx, and

palate; blood pressure

Motor to pharyngeal muscles (swallowing),

salivary gland (parotid


Cranial Nerves

X. Vagus: mixed (the major parasympathetic

nerve)

Sensory from pharynx, ear, diaphragm,

visceral organs in thoracic and abdominal

cavities

Motor to palatal and pharyngeal muscles

(swallowing and voice); to viscera in thoracic

and abdominal cavities


Cranial Nerves

XI. Accessory: motor to voluntary muscles

including sternocleidomastoid and trapezius

(move head, shoulders)

XII.Hypoglossal: motor to tongue (swallowing

and speech)


Aging

Rapid brain growth during first few years of

life

Due to increase in size of neurons and

proliferation of neuroglia

Increase in development of dendritic branches

and synaptic contacts

From early adulthood through old age:

Decline in brain mass

Fewer synaptic contacts brain function

Some decrease in brain function

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