A&P Chapter 11: Nervous System Divisions

Central Nervous System

• consists of the brain and spinal cord

Meninges

• membranes that protect the brain and spinal cord

• 3 layers

Dura Mater

• outer mater layer of meninges

Arachnoid Mater

• middle layer of meninges

• Web-like layer

Pia Mater

• deepest inner layer of meninges

Ventricles

• places where CSF is produced

• Continuous with the central canal of the spinal cord

• 4 of them

The 4 ventricles

• 2 lateral ventricles (1st and 2nd ventricles)

• 3rd ventricle

• 4th ventricle

Interventricular foramina

• connects the 3rd ventricle to the lateral ventricle

Cerebral Aqueduct

• connects the 3rd and 4th ventricles

Cerebrospinal Fluid (CSF)

• secreted by the choroid plexuses

• Selective transfer of substances from blood to form

• Nutritive and protective of CNS neurons

• Maintains stable ionic concentrations in the CNS

Places CSF cirulate

• ventricles

• Central canal

• Subarachnoid space

Arachnoid granulations

• absorbs the CSF after it exchanges substances

Volume of CSF at a time

About 140 mL

Choroid Plexuses

• special capillaries of pia mater covered by ependymal cells

Traumatic Brain Injury (TBI)

• result of mechanical force to the CNS

• Fall, attack, accident, or sports injury

Concussion

• mild TBI

• Results from a one time injury

• No lasting symptoms

Chronic Traumatic Encephalopathy (CTE)

• mild repetitive TBI

• Usually sports related

• Small injuries to the NCS over time

• Symptoms have long lasting effects

Blast-related Brain injury

• severe TBI

• Explosion in combat situations

• Leads to cognitive decline years after injury

CSF Pressure

• secretion and absorption keeps CSF pressure constant

• Interference can increase intracranial pressure (ICP) in ventricles

• Can lead to collapse of cerebral blood vessels, injury of brain tissues compressed against the skull

Spinal tap

• aka lumbar puncture

• Used to measure CSF pressure

Brain

• neural centers for sensory info

• Sensations and perceptions

• Motor commands to skeletal muscles

• Higher mental functions

• Coordinating muscular movement

• Regulating visceral activities

• Personality

Major Portions of the Brain

• Cerebrum

• Diencephelon

• Cerebellum

• Brainstem

Cerebrum

• largest part of the brain

Falx cerebri

• separates the two hemispheres of the cerebrum

Corpus Callosum

• connects the two cerebral hemispheres

Gyri

• ridges or convolutions

Sulci

• shallow grooves in a surface

Fissures

• deep grooves in a surface

Longitudinal fissure

• Fissure that separates the cerebral hemispheres

Transverse fissures

• fissure that separates the cerebrum from the brainstem

5 lobes of the cerebral hemispheres

• frontal lobe

• Parietal lobe

• Temporal lobe

• Occipital lobe

• Insula

Insula

• only lobe not named for the bone lying above it

• Deep within the lateral sulcus

Cerebral Cortex

• thin. Layer of gray matter

• Makes up outermost layer of all outer lobes of cerebrum

• Contains 75% of neuron cell bodies in the nervous system

White matter of the Cerebrum

• under the cerebral cortex

• Most of cerebrum

• Bundles of myelinated axons connects neuron cell bodies in cerebral cortex to other portions of nervous system

Functions of cerebral cortex

• interpreting impulses from sensory organs

• Initiating voluntary movements

• Storing info as memory

• Retrieving stored info

• Reasoning

• Seat of intelligence and personality

Central Sulcus

• sulci that separates brain into front and back

Motor Area

• groove above central sulcus for motor function

Sensory Area

• groove below central sulcus for sensory function

Associations Areas of the Cortex

• regions not primarily motor or sensory

• Connect to each other and to other structures in brain

• Widespread throughout cerebral cortex

• Analyze and interpret sensory experiences

• Provide memory, reasoning, verbalization, judgement and emotions

Dominant Hemisphere

• most people are left hemisphere dominant

• Controls language skills of speech, writing and reading

• Verbal, analytical and computational skills

Non dominant Hemisphere

• controls nonverbal tasks

• Motor tasks involving orientation in space

• Understanding and interpreting musical and visual patterns

• Provides emotional and intuitive thought processes

Short term (working) memory

• neurons connected in a curcuit

• Circuit stimulated over and over

• When impulse flow ceases, memory does also

Memory consolidation

• way memories enter long term memory

Long Term Memory

• holds more memory than short term

• Lasts a lifetime

• Changes structure or function of neurons

• Makes new synaptic connections by increasing branching of processes

Long term potentiation

• increase in neurotransmitter release and effectiveness of synaptic transmission upon repeated stimulation

Diencephalon

• between cerebral hemispheres and above brainstem

• Surrounds third ventricle

• Composed of gray matter

Portions of diencephalon

• thalamus

• Hypothalamus

• Optic tracts

• Optic chiasma

• Infudibulum

• Posterior pituitary

• Mammillary bodies

• Pineal gland

Thalamus

• gateway for sensory impulses ascending to cerebral cortex

• Receives all sensory impulses (except for smell)

• Channels impulse to appropriate part of cerebral cortex for interpretation

Hypothalamus

• maintains homeostasis by regulating visceral activities

• Links neurons and endocrine systems

Limbic system

• several structures in various parts of the brain

• Controls emotional responses, feelings, behavior oriented toward survival

• Reacts to potentially life-threatening upset

Brain Stem

• connects brain to the spinal cord

Parts of the brainstem

• midbrain

• Pons

• Medulla oblongata

Midbrain

• short section of brainstem

• Lies between Diencephalon and pons

• Contains bundles of fibers that join lower parts of brainstem and spinal cord with higher part of brain

Parts of midbrain

• cerebral aqueduct

• Cerebral peduncles

• Corpora quadrigemina

• Red nucleus

Cerebral peduncles

Main motor pathways that connect cerebrum to lower portions of nervous system

Corpora quadrigemina

• centers for visual and auditory reflexes

Red nucleus

• plays a role in postural reflexes

Pons

• Rounded bulge on underside of brainstem

• Between midbrain and medulla oblongata

• Relays nerve impulses between medulla oblongata and cerebrum

• Relays impulses from cerebrum to cerebellum

• Helps regulate rhythm of breathing

Medulla Oblongata

•Enlarged continuation of spinal cord

•Conducts ascending and descending impulses between brain and spinal cord

•Contains cardiac, vasomotor, and respiratory control centers

•Contains various nonvital reflex control centers (coughing, sneezing, swallowing, and vomiting)

• Injuries are often fatal

Reticular Formation

•Also called Reticular Activating System

•Complex network of nerve fibers scattered throughout brainstem

•Extends into the diencephalon

•Connects to centers of hypothalamus, basal nuclei, cerebellum, and cerebrum with ascending and descending tracts

•Filters incoming sensory information, passing some to cerebral cortex, and discarding unimportant information

•Arouses cerebral cortex into state of wakefulness

• Decreased activity causes sleep

Types of Sleep

• Non-REM Sleep

• REM Sleep

Non-REM Sleep

•Slow wave sleep

•Person is tired

•Decreasing activity of reticular formation

•Restful and dreamless

•Reduced blood pressure and respiratory rate

•3 stages, ranging from light to heavy

• Alternates with REM sleep

REM Sleep

•Called paradoxical sleep, because some areas of brain are active

•Heart and respiratory rates irregular

• Dreaming occurs

Cerebellum

•Inferior to occipital lobes

•Dorsal to pons and medulla oblongata

•Two hemispheres separated by falx cerebelli

•Vermis connects hemispheres

•Cerebellar cortex (gray matter)

•Arbor vitae (white matter)

•Cerebellar peduncles

•Dentate nucleus (largest nucleus)

•Integrates sensory information concerning position of body parts

•Coordinates skeletal muscle activity

•Maintains posture

Recent studies suggest other possible roles for the cerebellum. These include interaction with other parts of cerebral cortex, such as the limbic system and the auditory areas.

Electroencephalogram (EEG)

• records fluctuating electrical charges in the brain (brain waves)

4 types of brain waves

• Alpha

• Beta

• Theta

• Delta

Alpha Brain Waves

• awake

• Resting

• Eyes closed

Beta Brain waves

• active mental activity

• Under tension

Theta Brain Waves

• mostly in children

• In some adults during sleep or stress

Delta Brain Waves

• mainly during sleep

Spinal Cord

•Slender column of nervous tissue continuous with brain and brainstem

•Extends downward through vertebral canal

• Begins at the foramen magnum and terminates at the first and second lumbar vertebrae (L1 to L2) space

Longitudinal section portions of the spinal cord

• cervical enlargement

• Lumbar enlargement

• Conus medullaris

• Filum terminale

• Cauda equina

Cervical enlargement

• enlargement that supplies nerves to the upper limbs

Lumbar enlargement

• enlargement that supplies nerves to lower limbs

Conus Medullaris

• tapering region below lumbar enlargement

Filum Terminale

• cord of connective tissue that anchors spinal cord to cocyx

Cauda Equina

• group of lumbar and sacral nerves extending downward from conus medullaris in vertebral canal

Functions of the Spinal Cord

• center for spinal reflexes

• Conduits for impulses to and from the brain

Monosynaptic reflex

•Contains 2 neurons, sensory and motor

•Has only 1 synapse in spinal cord

•Example:  Patellar or knee-jerk reflex

Helps maintain an upright posture

Withdrawal Reflex

•Occurs when person touches or steps on something painful (stove, tack)

• Prevents or limits tissue damage, by removing limb from painful stimulus

• Polysynaptic

• Reciprocal innervation

Crossed Extensor Reflex

•During withdrawal reflex, flexors on affected (ipsilateral) side contract, and extensors are inhibited

•At same time, extensors on opposite (contralateral) side contract, flexors are inhibited

• Also shifts body weight, so person remains upright

Ascending Tracts

• conduct sensory impulses to the brain

Descending tracts

• conduct motor impulses from the brain via motor neurons reaching muscles and glands

Amyotropic Lateral Sclerosis (ALS)

•Also called Lou Gehrig’s Disease or motor neuron disease

•Involves degeneration of motor neurons in spinal cord, brainstem, cerebral cortex

•Possible causes:  overactive microglia that kill neurons, or buildup of oxygen-free radicals that neurons or astrocytes cannot counter

•Symptoms:  Speaking difficulties, dragging foot, clumsiness, fatigue, coordination issues, muscle twitches, weakness

•Cognitive function usually remains normal

•Usually fatal in 2 to 5 years, due to respiratory problems

•10% of cases are inherited

No cure

Spinal Cord Injuries

•Most common causes are workplace and motor vehicle accidents

•Severity depends on extent and location of damage

•Compression or distortion of the spinal cord can result in damage to or death of neurons, leading to pain, weakness, loss of sensation, and muscular atrophy

•CNS neurons do not regenerate

•Injury to ascending tracts can result in loss of sensation

•Injury to descending tracts can result in loss of motor function, paralysis

Research is looking into ways of limiting damage after injury: growth factors, stem cells

Endoneurium

• loose connective tissue that surrounds individual axons

Perineurium

• loose connective tissue that surrounds fascicles

Epineurium

• dense connective tissue that surrounds a group of fascicles

Cranial Nerves

• 12 pairs of nerves on the underside of the brain

• Some sensory nerves

• Some motor nerves

• Some both

• I to XII, anterior to posterior

Spinal Nerves

• All except for first are mixed nerves

• 31 pairs

• 8 cervical

• 12 thoracic

• 5 lumbar

• 5 sacral

• 1 coccygeal

Cauda equina

Formed by descending roots of lumbar, sacral and coccygeal nerves

Dermatome

• area of skin innervated by sensory nerve fibers of a particular spinal nerve

Nerve Plexus

• complex network formed by anterior rami (branches) of spinal nerves

• 3 nerve plexuses

• Cervical

• Brachial

• Lumbosacral

Whiplash

• sudden bending of neck

• Compression of cervical plexus nerves

• Leads to persistent headache

• Pain in neck

Broken/dislocated vertebrae in neck

• can sever or damage axons leading to phrenic nerves

• Result in paralysis of diaphragm

Thoracic outlet syndrome

• pressure on brachial plexus

• due to continuous flexion of arm (as in painting or typing)

• results in pain in neck, shoulder, upper limb

Sciatica

• compression of intervertebral disc in lumbar region

• results in pain in lower back, gluteal region, and perhaps thigh, calf, foot

Carpal Tunnel Syndrome

• repeated movements of hand inflame tendons that pass through carpal tunnel (space between bones in wrist)

• swelling in tendons compresses median nerve

• resulting in pain in the arm, wrist

Autonomic Nervous System (ANS)

• efferent (motor) part of peripheral nervous sytstem

• Controls visceral activities

• Regulates smooth and cardiac muscles and glands

• Homeostasis

• Respond to stress

Divisions of ANS

• sympathetic division

• Parasympathetic division