Unit IV: CoordinationImpulse Transmission

Ch. 11 – pgs 373-389

Ch. 14 – pgs 471-487

Review

1. What is the CSF and what are the three functions it provides?

2. Which way is caudal?

3. Which is not a region the spinal nerves are named for? a.) cervical, b.) thoracic, c.) pelvic, d.) lumbar, e.) sacral

4. How does the location of white and gray matter differ in the spinal cord compared to the cerebrum?

5. The formation of the blood-brain barrier is stimulated by which glial cells?

6. _____ are folds that increase surface.

7. By increasing surface area, they allow for more ___________.

Initiation of Nerve Impulses

Resting Membrane Potential• ICF relative to ECF – electrical potential• Polarized• Requires use of ATP• Created by Na+-K+ pumps

ECF

ICF

Na+

channel

K+

channel

Na+ 145 mEq/LK+ 4 mEq/L

Na+ 12 mEq/LK+ 150 mEq/LLarge anionsthat cannotescape cell

Initiation of Nerve Impulses

Action Potentials1. Na+ gate opens; K+ gate

begins to open; depolarization begins

2. Na+ gate closes; K+ gate opens fully; repolarization begins

3. Both Na+ gate and K+ gate closed; repolarization complete.

Extracellular fluid

Plasmamembrane

Cytosol Gatedchannel(closed)

Resting state Arrival of ACh

Bindingsite

Gated channel opens

AChACh

Initiation of Nerve Impulses

Types of gated channels:• Chemical gated channel

• Voltage gated channel

Channel inactivatedChannel closed Channel openInactivationgate

Activationgate

Restingpotential

Gradedpotential

Presynaptic neuron

stimulusproduces

mayproduce

Action potential

Postsynaptic cell

triggers

Informationprocessing

Syna

ptic

act

ivity

Initiation of Nerve Impulses

Notes• Threshold – • Depolarization – • Refractory period – • Action Potentials –

– follow an All or Nothing Law– are nondecremantal– are irreversible

Conduction of Nerve ImpulsesNotes• Unmyelinated fibers – continuous propagation• Myelinated fibers – ions exchanged only at nodes of Ranvier

– Saltatory propagation

+ ++ +

+ +

+ +

+ +

+ +

+ ++ +

+ +

+ +

+ +

+ +

+ ++ +

+ +

+ +

+ +

+ +

– –– –

– –– –

– –– –

– –– –

– –– –

+ +

+ +

– –– –

+ +

+ +

– –– –

– –– –

+ +

+ +

– –– –

– –

– –

– –

– –

– –

– –

(a)

(b)

Na+inflow at nodegenerates action potential(slow but nondecremental)

Na+ diffuses along insideof axolemma to next node(fast but decremental)

Excitation of voltage-regulated gates willgenerate next actionpotential here

+ +

+ +

– –– –

+ +

+ +

– –– –

+ +

+ +

– –– –

+ +

+ +

– –– –

+ +

+ +

– –– –

+ +

+ +

– –– –

Action potentialin progress

Refractorymembrane

Excitablemembrane

Synaptic TransmissionChemical Synapse Structure

• Synaptic knob

• Synaptic vesicles

• Synaptic cleft

–20-40nm gap

• Neurotransmitter receptors

Synaptic Transmission

Synaptic delay (0.5 msec)

Classes of Neurotransmitters

– Excitatory, inhibitory, neuromuscular junction

3 kinds of synapses:

• Excitatory cholinergic synapse = ACh

• Inhibitory GABA-ergic synapse = GABA

• Excitatory adrenergic synapse = NE

Excitatory Cholinergic Synapse

Mitochondrion

AcetylcholineSynapticvesicle

SYNAPTICKNOB

SYNAPTICCLEFT

POSTSYNAPTICMEMBRANE

Choline

Acetate

Acetylcholinesterase(AChE)

AChreceptor

CoAAcetyl-CoA

Nerve signal opens voltage-gated calcium channels in synaptic knob

Ca+ triggers release of neurotransmitter.

ACh binds to sodium channel receptors producing a graded depolarization.

ACh is broken down into acetate and choline by AChE.

Choline is reabsorbed and used to synthesize new molecules of ACh.

1

2

3

4

5

Inhibitory GABA-ergic Synapse

• Nerve signal triggers release of neurotransmitters

• Receptors trigger opening of Cl- channels

• Postsynaptic neuron now less likely to reach threshold

Excitatory Adrenergic Synapse

cAMP

Enzyme activation

Genetic transcription

Enzyme synthesis

Na+

Adenylate cyclase

G protein–

+

–

+

–

+

Postsynaptic neuron

Presynaptic neuron

Norepinephrine

2 3

4

5

1

6

7

Neurotransmitterreceptor

Ligand-regulatedgatesopened

Multiplepossibleeffects

Metabolicchanges

ATP

Postsynapticpotential

• Acts through 2nd messenger systems (cAMP)

• cAMP has multiple effects

– binds to ion gate inside of membrane

– turn metabolic pathways on/off

– induces genetic transcription

• Its advantage is enzymatic amplification

Cessation of the Signal

1. Stop signal in presynaptic neuron

2. Mechanisms to “turn off” the signal

– diffusion of neurotransmitter into ECF

– synaptic knob reabsorbs neurotransmitters

– degradation of neurotransmitters in synaptic cleft

• Acetylcholinesterase

• Adrenalate cyclase

Temporal Summation

Initialsegment

Thresholdreached

ACTIONPOTENTIAL

PROPAGATIONFIRST

STIMULUSSECOND

STIMULUS

Postsynaptic Potentials

• Excitatory postsynaptic potentials (EPSP)

– a positive voltage change = more likely to fire

• Inhibitory postsynaptic potentials (IPSP)

– a negative voltage change = less likely to fire

• Summation – net postsynaptic potentials

Spatial Summation

TWOSIMULTANEOUS

STIMULI

ACTIONPOTENTIAL

PROPAGATION

Thresholdreached

Peripheral Nervous System

• Consists of spinal and cranial nerves

• Sensory (afferent) Division

–Somatic Sensory Division

–Visceral Sensory Division

• Motor (efferent) Division

–Somatic Motor Division

–Visceral Motor Division (Autonomic Nervous System)

• Sympathetic Division

• Parasympathetic Division

• Enteric Division

Motor DivisionAutonomic vs. Somatic Reflex Arcs

1. ANS = 2 neurons from CNS to effectors

• preganglionic neuron - cell body in CNS

• postganglionic neuron - cell body in peripheral ganglion

Motor DivisionAutonomic vs. Somatic Reflex Arcs

2. Autonomic effectors function in absence of stimulation

3. Autonomic stimulation can be excitatory or inhibitory

4. Autonomic control is usually involuntary

5. Autonomic effectors are smooth and cardiac muscle, glands

6. Autonomic integrative center in hypothalamus

Autonomic Nervous SystemSympathetic Division

1. Origin in thoracolumbar region

2. Short preganglionic fibers, long postganglionic fibers

3. Synapses at paravertebral ganglia

4. 17 postganglionic neurons for every preganglionic neuron

5. Mass activation

6. “Fight or Flight”

Associated with adrenal glands

• Stimulate the release of neurotransmitters

PONS

Eye

Salivaryglands

Heart

Lung

Liver andgallbladderStomach

SpleenPancreas

LargeintestineSmallintestine

AdrenalmedullaKidney

Urinary bladderScrotumPenis

Uterus

Ovary

Inferiormesentericganglion

Superior mesentericganglion

Celiac ganglion

Cardiac andpulmonary plexuses

T1T1

L2L2

Spinalcord

Postganglionic fibers tospinal nerves (innervatingskin, blood vessels, sweatglands, arrector pilimuscles, adipose tissue)

Sympatheticchain ganglia

Preganglionic neuronsKEY

Post-Ganglionic neuronsSympathetic Efferent Pathways

Autonomic Nervous SystemParasympathetic Division

1. Origin in craniosacral region

2. Long preganglionic fibers, short postganglionic fibers

3. Synapses at terminal ganglion

4. 2 postganglionic neurons for every preganglionic neuron

5. Specific and local effects

6. “Rest and Digest”

Spinalcord

S2

S3

S4

Uterus Ovary

Penis

Scrotum

Liver andgallbladderStomach

Spleen

Pancreas

LargeintestineSmallintestine

Kidney

Urinary bladder

Rectum

Eye

Salivary glands

Heart

Lungs

Hypogastricplexus

Inferior mesentericplexus

Celiac plexus

Cardiac plexus

Vagus nerve (X),which providesabout 75% of all parasympathetic outflow

PONS

Otic ganglion

Submandibularganglion

Ciliary ganglion

Pterygopalatine ganglion

III

VII

IX

Lacrimal gland

Preganglionic neuronsKEY

Ganglionic neuronsParasympathetic Efferent Pathways

Innervation

Dual Innervation

• Antagonistic Effect

• Cooperative Effects

Brain

Spinal cord

Iris

Pupil

Pupil dilated Pupil constricted

Parasympathetic fibersof oculomotor nerve (III)

Sympatheticfibers

Ciliaryganglion

Superiorcervicalganglion

Cholinergic stimulationof pupillary constrictor

Parasympathetic(cholinergic) effect

Sympathetic(adrenergic) effect

Adrenergicstimulation ofpupillary dilator

Innervation

Control without dual innervation

• Some targets receive only sympathetic fibers

• Sympathetic tone

Artery

1

1

2

3

3

1

2

3

2

2

3

1

Strongsympathetictone

Smooth musclecontraction

Vasoconstriction

Weakersympathetictone

Smooth musclerelaxation

Vasodilation

Sympatheticnerve fiber

Vasomotortone

(a) Vasoconstriction

(b) Vasodilation