The Nervous System

NS and Endocrine System

•Transmit info from 1 part of body to another

Communication—Integration--Control

Nervous System

•Rapidly & short duration via nerve impulses

Endocrine System

•Slowly via hormones (chemicals) secreted by

ductless glands into blood stream circulated

from glands to other parts of the body (target cells)

Homeostasis: Balanced & Controlled internal

environment of body essential to fx of

all body systems

relies on physiological control &

integration

NS: Monitors & Responds to In/External stimuli

Nervous System

brain & spinal cord nerves & associated

cells not part of CNS

CNS PNS

Motor Nerves Sensory Nerves

Respond to stimuli from Env

Sensory Receptors w/in sense organs

(Eyes, Ears, Taste, Touch, Smell)

Somatic NS Autonomic NS

To skeletal muscles/voluntary

To cardiac & smooth muscles, glands, involuntary

sympathetic parasympathetic

Fight/Flight

Antagonistic

gas ↑ brake ↓

Coverings & Fluid Spaces of Brain & Spinal Cord

Meninges: Tough, fluid containing membrane

surrounded by bone (skull & vertebrae)

3 Layers of Spinal Meninges

Dura Mater (tough outer layer, lines vertebral canal)

Pia Mater ( innermost layer covering spinal cord)

Arachnoid Layer ( middle layer between Dura & Pia)

cob web like w/ fluid (CSF) filling spaces

Meninges (protective) extend up & around enclosing brain

Fluid fills Arachnoid spaces of brain meninges & spinal cord

Cerebral Ventricles: Fluid filled spaces w/in brain

2 lateral ventricles deep w/in brain

w/in Lt & Rt cerebrum

(lgst part of brain conscious, voluntary,

mental processes, emotions)

CSF: cerebral spinal fluid forms continuously from fluid

filtering out of blood

network of brain capillaries (choroid plexus) & into

ventricles

From lateral ventricles CSF 3rd ventricle & flows ↓

aqueduct of Sylvius 4th ventricle subarachnoid

spaces subarachnoid spaces of meninges that

surround spinal cord blood via veins in the brain

***CSF forms continuously from blood, circulates & is reabsorbed into blood again

**Pressure on Aqueduct of Sylvius (Ex. brain tumor) blocks return path of CSF blood

CSF accumulates in ventricles or meninges.

Hydrocephalus water on the brain

Treatment catheter to drain fluid back to body

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3 Types of Neurons

Sensory Neurons (Afferent): Carry impulses from sense

organs to spinal cord/brain (CNS)

Dendrites can be very long

Motor Neurons (Efferent): Carry impulses from CNS (brain/sc)

(Effecter) to muscles & glands

Interneurons (Central or Connecting): Connect sensory & motor

neurons in spinal cord

Lie w/in gray matter of

CNS

Cells of the Nervous System

Neurons & Neuroglia Basic Neuron Structure

sensory, motor, &

interneurons (between

sensory & motor

neurons in spinal column)

Impulse received by dendrites

Saltatory conduction

**vertebrates

Soma

Cell body

Axon terminals vesicles w/ neurotransmitters

Many dendrites

Myelinated axon carries impulse from cell body axon terminals

Saltatory Conduction: carries impulse node to node (vertebrates)

200 m/s vs few mm/s in unmyelinated (gray matter)

Mostly outside CNS

80% lipid 20% protein

Insulated sheath

White Matter

Indentations between

Schwann cells

Extend thru axon from cell body

Axons in brain & sc have no neurilemma no regeneration but those in nerves do regeneration

Neuroglias (connective tissue)

Special connecting & supporting tissues of brain & spinal cord don’t transmit impulses

Glia (glue): hold neurons together & protects them

Glioma: common type of brain tumor develops from

neuroglia cells

3 Types of Neuroglia

Astrocytes:

Microglia: usually stationary can move & become phagocytic

(scavengers)

Oligodendroglia: hold nerve fibers together & produce fatty

myelin sheath that covers nerve fibers (axons) in brain &

spinal cord (not Schwann Cells outside CNS)

Myelinated fibers (high fat white matter)

Nonmyelinated (gray matter)

Myelin Disorder Diseases associated with Oligodendroglia

Multiple Sclerosis: Most common 10 of CNS

Characterized by myelin loss/ destruction

w/ oligodendroglial cell injury/death

demyelination of white matter of CNS

nerve conduction impaired

weakness, in-coordination, visual impairment,

speech disturbances

Afflicts more women between 20-40

MS ??? Related to autoimmunity & viral type infections

Prolonged disease w/ relapses & remissions

White Matter in brain & Spinal cord made up of Tracts

Tract: bundle of myelinated axons

White Matter outside brain & spinal cord = nerves

Nerves bundles of myelinated axons

single group of nerve fibers surrounded by

connective tissue sheath

Nerve Trunk group of bundled nerves

7 cervical vertebrae

12 thoracic vertebrae

5 lumbar vertebrae

Fused vertebrae

8

12

5

5

1 coccyx

Nerve prs

Reflex Arcs impulse conduction in 1 Direction

2 neuron arc (sensory motor)

3 neuron arc (sensory interneuron motor neuron)

Interneurons w/in gray matter (H-zone)

Synapse: (microscopic space between neurons that

neurotransmitters released from axon terminals

diffuse across)

Sensory neuron receptors w/ dendrites pick up stimulus

impulse created cell body axon of sensory neuron

Synapse interneuron (dendrite cell body axon)

synapse motor neuron (dendrite cell body axon)

neuromuscular junction

Posterior root ganglion

Anterior root spinal nerve

Patellar Tendon Knee Jerk Reflex

Infant Reflexes

Rooting Reflex: stroke cheek/ turns head towards touch

Gripping Reflex: grasp anything placed in palm

Toe Curling Reflex: Inner sole of foot stroked toes curl

Outer sole of foot stroked toes spread

Stepping Reflex: Held up w/ feet on surface walk/march

Sucking Reflex: when something touches roof of mouth

Startle/Moro Reflex: sudden sound/mvmt throw arms &

legs out & head back then pull limbs back into body

Galant Reflex: stroke middle or lower back body curves

towards side stroked

Tonic Neck Reflex: place on stomach whichever side head is facing limbs on that side straighten, opposite side curl

The Nerve Impulse

Initiated by a stimulus (pressure, temp, chemical changes, etc)

Resting Neuron Outisde +++ (Resting Potential)

Inside ---

Na+ ions pumped out and K+ ions pumped in

Na/K pump run by ATP Active Transport

More K+ ions leak out than Na+ ions leak in creating

+++ Outside c.m Resting Potential

--- Inside c.m

(Also other ions present Ex. Cl-)

C.M has gates/channels that allow ions to pass thru

normally closed

Steps of an Action Potential (Nerve Impulse)

Neuron stimulated nerve impulse generated

Na+ gates open & flow inside C.M.

Inside becomes more + than outside Action Potential

Nerve Impulse

Depolarization

As impulse passes, K+ gates open and K+ ions flow out

Inside becomes – and outside + again (Reploarization)

Threshold: minimal level of stimulus required to create

impulse All or none

Impulse moves in 1 direction b/c Na+ gates close after impulse & can’t be reopened for short time (Refractory Period)

http://www.blackwellpublishing.com/matthews/actionp.html

Link to Action Potential Animation w/ Saltatory Conduction

Resting Potential

Action Potential Na+ rush in Depolarization

Re-polarization – Action Potential – Resting Potential

Re-polarization

Refractory Period

Resting Potential

Action Potential reaches Axon Terminal

Vesicles w/ neurotransmitters rupture chemicals released diffuse across synaptic cleft (assist, stimulate or inhibit postsynaptic neurons)

Neurotransmitters: chemicals used by neuron to transmit impulse across synapse to another neuron or cell (Ex. muscle)

*neuromuscular

junction

• Impulse arrives at axon terminal

•Vesicles release neurotransmitters into synaptic cleft/gap

•Neurotransmitters diffuse across synapse & attach to

receptors on next cell

•Stimulus causes rush of Na+ to rush into cell

•If threshold met/exceeded new impulse or Rx occurs

Ex. muscle contraction

Neurotransmitters quickly: broken ↓ by enzymes

taken up/recycled by axon terminal

diffuse away

Certain Illnesses associated w/ abnormal levels of Neurotransmitters

Depression: ↓ serotonin & norepinephrine

(Exercise releases these)

Schizophrenia: associated w/ ↑ levels of dopamine

Parkinson’s Disease: progressive NS disease most often after age of 50, associated with the destruction of brain cells that produce dopamine, characterized by muscular tremor, slowing of movement, partial facial paralysis, peculiarity of gait and posture.

Endorphins & Enkephalins: Inhibit conduction of pain

impulses

How do abnormal levels of neurotransmitters affect Fx of NS?

Either ↑ or ↓ transmission of nerve impulse

Nerve Gas: Class of Lethal Weapons

Fx: Inactivate certain enzymes of nerve transmission

Normal: neurotransmitters diffuse away, recycled, inactivated

Neurotransmitter Acetylcholine is inactivated by cholinesterase enzymes that deactivate acetylcholine quickly efficient, precise synaptic transmission

Nerve Gas: binds to & inhibits cholinesterase so acetylcholine remains in synapse continuous stimulation of nerves

Uncontrollable convulsions, muscular contractions, death

Synaptic Integration: Provides checks & balances in NS

At each neuron, Excitatory & Inhibitory receptors compete for membrane control

Signals can totally/partially cancel each other out or augment each other’s effect

Net outcomes depend on strength, direction & location of each signal.

Clostridium tetani Produces toxin that interferes w/ Inhibitory Receptors & Motor Neurons in CNS (brain/sc)

Lock jaw unbalanced excitation of muscle cells

constant (tetanic) contraction spastic paralysis death

Structure of the Spinal Cord

• Avg adult spinal cord 17-18” long

• Lies inside spinal column in spinal cavity

• Extends from occipital bone to 1st lumbar vertebrae

• Hands on hips L4

• Spinal meninges extend beyond spinal cord

almost to end of spinal column

• Allows for spinal tap (lumbar puncture) to extract CSF (test)

insert needle just above L4

Spinal Cord

• H- shaped gray matter ( dendrites & cell bodies of neurons)

• White matter outer part (bundles of myelinated nerve fibers) spinal tracts

• Ascending tracts conduct impulses ↑ cord to brain Ex. sensory fx (pain, touch pressure, etc)

• Descending tracts conduct impulses ↓ cord from brain Ex. vol. mvmts, skeletal muscle activity

Spinal Cord fxs as Switchboard

Carries impulses to & from brain

To brain via ascending tracts

From brain via motor tracts

Contains centers for Reflex Arcs

Interneurons switch/transfer incoming sensory impulses

to outgoing motor impulses Spinal Cord Reflex Arc

2 kinds withdrawal reflex (Ex. from hot/sharp surface)

knee jerk reflex

Injury cuts spinal cord across impulses can’t pass produces

Loss of sensation Anesthesia

Loss of ability to move paralysis

Spinal Nerves (31 prs)

8 cervical (7 cervial vertebrae)12 thoracic (12 thoracic vertebrae)5 lumbar 5 (5 lumbar vertebrae)Sacrospinal (fused vertebrae)1 coccygeal (coccyx)

Conduct impulses between spinal cord & areas not supplied by 12 cranial nerves

Contain both sensory & motor fibers sensation mvmt

7 cervical vertebrae

12 thoracic vertebrae

5 lumbar vertebrae

Fused vertebrae

8

12

5

5

1 coccyx

Nerve prs

Dermatome: skin surface area supplied by single nerve

Herpes Zoster/Shingles: viral infection of single dermatome caused by varicella zoster virus of chicken pox

Virus travel thru cutaneous nerve & remains dormant in dorsal root ganglion long after chicken pox infection

↓ Immune Response (Ex. elderly, stress, radiation, immunosuppresive drugs virus may reactivate

Virus travels over sensory nerve to skin of single dermatome painful eruption vesicles, crust & clear 2-3wks

http://www.cafepress.com/apparelyzed/434981

PNS

Outside CNS

Nerves & associated cells not part of CNS (brain & s.c)

Consists of: cranial nerves that pass thru skull

stimulate head & neck

Spinal nerves: 31 prs

Ganglia: (nerve cell bodies)

Sensory Division of PNS: transmits impulses from sense organs CNS

Motor Division of PNS: transmits impulses from CNS muscles/glands (Effectors)

Somatic NS voluntary

Skeletal muscle contraction

Some also use reflex arc

Autonomic NS Involuntary

Ex. smooth muscles, digestion

pupils reflex

Sympathetic

↑ Effect (gas)

Parasympathetic

↓Effect (brake)

Running: Sympathetic NS ↑ heart rate, blood flow to skeletal

muscles, stimulates sweat & adrenal glands

Parasympathetic NS ↓ smooth muscle contractions

in digestive system

Stop Running: Parasympathetic NS ↓ heart rate & blood

flow to skeletal muscles

Sympathetic NS ↑ contractions of smooth

muscles in digestive system

Important Fx Maintaining Homeostasis

Divisions of the Brain

Billions of Neurons

1.4kg Must have continuous supply of O2

Part of brain that is damaged determines effects

Wavy bumps/folds: gyri (gyrus)

Shallow grooves: sulci (sulcus)

Folds/Grooves ↑S.A for more neurons

(S&F)

Gyri: folds

Sulci: grooves

Cerebrum: Largest part of brain

Voluntary, Conscious activities

Intelligence, Learning, Judgment

Divided into LT & RT hemispheres

by deep longitudinal fissure

Hemispheres connected by corpus callosum

Each hemisphere divided into 4 lobes

named after skull bones

Frontal (vol muscle mvmt)

Parietal (behind frontal)

Temporal (sides)

Occipital (back)

Myelinated fibers join

LT & RT HemispheresFx produces automatic mvmts & posture

Parkinson’s disease of basal ganglia shaking/tremors

Each ½ of Cerebrum deals w/ opposite side of body

• Sensations from LT body Rt hemisphere

• Sensations from RT body Lt hemisphere

Commands to move muscles also opposite

• LT hemisphere controls RT side of body

• RT hemisphere controls LT side of body

Studies suggest

RT hemisphere associated w/ artistic/creative

Lt hemisphere associated w/ analytical/mathematical

2 Layers to Cerebrum

Outer Cerebral Cortex gray matter (densely pkd cell

bodies & unmyelinated axons)

Processes info from sense organs

Controls body mvmts

Inner Cerebral Medulla white matter (bundles of

myelinated axons)

Connects Cerebral Cortex

& Brain Stem

3 Regions of Cerebral Cortex (Outer layer of Cerebrum))

Spinal Cord damage disconnects

ascending & descending tracts

Motor Centers: Instructions for motor response coordinated

Motor Cortex connects to Descending Motor Tracts

Stimulation of different point on Motor Cortex

muscles in different parts of body to contract

*** Lg area of motor cortex devoted to muscles that control

tongue & thumb mvmts Reflects amount of control

req’d for hand mvmts & speech

Regions of Motor Cortex cont’d

10 Receiving Centers: Receive sensory input from PNS

(Sensory) Somatic Sensory Cortex

(behind motor cortex)

is 10 receiving center for sensory

input from skin & joints via

Ascending Tracts

Association Centers: Separate from Motor & 10 Rec. Centers

but connected to motor & sensory thru

neural pathways

Brain Studies

1940’s Wilder Penfield surgically exposed Cerebral Cortex

Used weak electrical stimulation on patients still awake

Brain pkd w/ neurons but NO pain receptors!!!!

Stimulated part of Cerebral Cortex at a time & patients described sensations

Motor Cortex = areas where stimulation muscle

contraction

Sensory Cortex = areas where stimulation taste, touch,

sound

Areas where stimulation memories = physical location of

memories

Sensory control

Sensory Neurons (Affecter) brings message to spinal cord

Neurons in spinal cord carry impulses to Thalamus

via Ascending Tracts

Thalamus: switching station relays impulses to Sensory Cortex (in Cerebrum) for action

Motor Cortex sends message ↓ spinal column via descending tracts to synapse w/ Motor Neuron (Effecter)

??? Cases where parts of spinal cord destroyed & still sensation at different parts of body, despite no connections to carry impulse to cerebral cortex!!!

Brain Studies

Hebel & Wiesel (Harvard) studied visual cortex in kittens

Thought all nerve connection in brain genetically determined

Kittens: Kept 1 eye closed since birth

Nerve connection failed to develop!!!

Other eye nerve connections developed normally

Determined: Pattern of connections depends on kinds of visual stimulation experienced in early development after birth

Concluded: Abnormal nerve development env. not genetic influence

Env & sensory input develops neural pathways (plasticity)

*Babies & visual stimuli ↑ visual stimuli ↑ Nerve Connections

Cerebellum: 2nd largest part of brain (outer gray, inner mostly white)

Back of skull

Commands to move come from Cerebral Cortex

but Cerebellum coordinates & balances actions of

muscles smooth, efficient, graceful mvmt

Involuntary

Damaged Cerebellum muscle weakness

↓ Coordination

Simple tasks (walk, run) difficult

Train Cerebellum to coordinate muscle use

Practice helps develop connections to Cerebellum

make task easier (but not under conscious control)

***Occupational Therapy Importance

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brainstem

Brain Stem Midbrain

Pons

Medulla Oblongata

Brain Stem

Foramen Magnum opening in occipital bone for spinal cord to pass thru

Medulla: Extension of spinal cord just inside cranial cavity

Gray & White matter intermingle Reticular [RAS]

Formation

Invol Fx’s (breathing, swallowing, heart rate,

coughing)

*Remember in spinal cord inner (H) = gray / outer = white

Pons: (middle/bridge) between Medulla & Midbrain

Links cerebral cortex & cerebellum

Midbrain: above Pons (vision & hearing)

Brain Stem is 2 way conduction path

Sensory fibers impulses spinal cord brain

Motor fibers impulses brain spinal cord

Many Vital Reflex Centers lie in Medulla of Brainstem

Cardiac, Respiratory, Vasomotor Centers

Impulses that control heartbeat

respirations

blood vessel diameter

Diencephalon: Between midbrain & cerebrum

Contains Hypothalamus & Thalamus

(below thalamus)

Hypothalamus: Contains Posterior pituitary gland

Control over Paraventricular & Supraotic Nuceli

All internal organs (2 clusters of neuron cell bodies)

Appetites Make hormones Posterior Pituitary

Body Temp Gland stores/ secretes into blood.

Hunger Ex. ADH affects urine

Thirst volume to maintain body’s H2O

Fatigue balance

*** Coordinates Nervous System & Endocrine System

Some Neurons in hypothalamus

Fx as Endocrine (ductless) Glands

Axons secrete Releasing Hormones into blood

RH’s control release of

Anterior Pituitary Hormones

that influence hormone secretion by

other Endocrine Glands

Thalamus (above hypothalamus)

• Helps produce sensations (relays impulses to cerebral

cortex from sense organs, (except smell)

• Associates sensations w/ emotions

• Arousal/alerting mechanism

Brain Waves

Brian neurons capable of Action Potential (electrical activity)

Voltage sensitive electrodes on scalp

record weak electrical current

EEG: Electroencephalogram

Records electrical activity on scalp

Measures average activity of thousands of neurons

general idea of brain activity

Sleep: Activity of Cerebral Cortex ↓ to lowest level

unconsciousness deep unresponsive to light sleep

RAS (Reticular Activating System)

Network of neurons in Medulla Oblongata (brain stem)

helps control consciousness

Level of RAS ↓ sleep begins

Special group of neurons in brainstem activate light sleep

During deep sleep

↓ in heart rate, BP, respiration rate, energy use

During REM (Rapid Eye Mvmt) sleep dreaming occurs

Memory

Short Term: Not permanent

Stored as pattern of nerve impulses

in Cerebral Cortex

Vanishes w/in few days

unless interesting or effort to remember

Long Term: More permanent

Some last lifetime

May require effort to recall

Can become part of person’s consciousness

Some patients w/ severe brain injuries keep long term memory (even w/ Cerebral Cortex damage)

Suggests long term memory stored in structure of brain itself