8/13/2019 Physio CNS 2006

1/21

VI. CNS

Metabolic and circulatory features of the brain and CNS

Electrophysiological properties of CNS neurons

Neurotransmitters I: localization, synthesis, storage and transport

Neurotransmitters II: release and neurotransmitter receptorsNeurotransmitters III: transduction of neurotransmitter signals in the CNS

The chemical senses: taste and smell

Auditory physiology

The vestibular system and somatosensory physiology

Somatosensory physiology: pain and temperature

Signal transduction and processing in the retinaSignal processing and perception in the visual system

Spinal reflexes

Descending control of movement and posture

Basal ganglia

Cerebellum and cerebral cortex

The reticular formation, reinforcement pathways, cortex, and EEGSleep-wakefulness

DOP: Higher cortical functions and imaging

Learning and memory

Lateralization of function, language and emotion

Hypothalamic function I and II

8/13/2019 Physio CNS 2006

2/21

CNS Physio

8/13/2019 Physio CNS 2006

3/21

Brain Metabolism and Circulation

5. Cerebral blood flow increases in cases of

a. influenza.

b. hypoxia (Arterial P02= 75 mmHg).

c. hypertension (Arterjal pressure= 140 mm Hg).

d. coma.

e. hypercapnia (Arterial PCO2 = 75 mmHg).

8/13/2019 Physio CNS 2006

4/21

Regulation of Cerebral Blood

Flow

60

120

60 120 180

Mean Arterial Blood Pressure (mmHg)

Cereb

ralBloodFlow

(ml/min/100g)

Autoregulation

of cerebral

blood flow

Hypercapnia

Sympathetic

nerve stimulation

Remember

Metabolic

Hyperemia!

8/13/2019 Physio CNS 2006

5/21

Electrophysiology of CNS Neurons

The resting membrane potential for all brain neurons is:

a. at an equilibrium state for potassium ions.

b. at an equilibrium state for sodium ions.

c. at an equilibrium state for chloride ions.

d. a steady- state level between the equilibrium potentials of the ionsinvolved, weighted by their relative permeabilities/conductances.

e. is the same as the resting membrane potential for brain glial cells.

Which of the following changes would increase the driving force for

sodium entry into a neuron?

a. depolarization of the membrane potential

b. hyperpolarization of the membrane potential

c. an increase in the extracellular sodium concentration

d. The sodium equilibrium potential ENabecomes more positive.

e. b, c and d are correct.

8/13/2019 Physio CNS 2006

6/21

Membrane Potential

Excitation is caused by:

Depolarization or Hyperpolarization

Increase in gK+or gNa+

Increase in ENa or EK

8/13/2019 Physio CNS 2006

7/21

Major Neurotransmitters

Name Effect Synthesis Degradation Location

GABA Inhibitory GAD from

Glutamate

Transported,

GABA-T

Ubiquitous

Glutamate Excitatory Gluatminase,

other

Transported Ubiquitous

Acetylcholine Excitatory Choline,acCoA, CAT

AchE Basal Foreb.

Hippocampus

Epi, NE, DA Excitatory

(except a1)

Tyrosine, TH Trans, MAO,

COMT

NE- LC,Teg.

DA- SN, Stri.

Serotonin(5-HT)

Excitatory Tryptophan,TH

Trans, MAO Pons Raphe

Histamine Excitatory Histidine,

(Decarboxyl)

Transferase,

MAO

Hypothalamus

Peptides Both Precursors Proteases Ubiquitous

8/13/2019 Physio CNS 2006

8/21

Catecholamine Synthesis

Tyr L-Dopa DA NE Epi

Tyr Hydroxylase AAAD DbH PNMH

MAO or COMT

MHPG, VMA, HVA

8/13/2019 Physio CNS 2006

9/21

Neurotransmitter Receptors

GABA GABAA

Postsynaptic Cl-channel

Agonists- Muscimol, Barbs, (Benzos)

GABAB G-protein-coupled, activates Adenylate Cyclase

Axoaxonal inhibition. Prevents NT release

GABAB

-

Pre

Post GABAA

GABA

GABA

GABA

-

GABA

GABA

NE

(-)

8/13/2019 Physio CNS 2006

10/21

Neurotransmitter Receptors

Ach Nicotinic

Cation Channel (Ca++in CNS)

Spinal Cord, Sup. Colliculus

Muscarinic G-protein-coupled, Giinactivates Adenylate

Cyclase, Gqactivates PLC- Ca++ influx

M1- striatum, hippocampus, cerebrum M2- cerebellum

8/13/2019 Physio CNS 2006

11/21

Somatosensory

Mechanoreceptors (Abafferents) Touch and Pressure (Slow Adapting)

Merkels Disk

Ruffini Corpuscles

Touch (Fast Adapting) Meissners (low-freq.)

Hair Follicle

Pacinian Corp. (high-freq.)- wide receptive field

Proprioception

Joint Receptors

Dorsal Column-Medial Lemniscus

8/13/2019 Physio CNS 2006

12/21

Pain Modulation

Nociceptive Fibers

(Ador C)synapse on

SC neurons in the

anterior horn (A). Descending 5-HT or

NE neurons can

modulate these

synapses to preventpain transmission.

8/13/2019 Physio CNS 2006

13/21

Temperature Sense

Cold (Ad) and Warm (C) fibers:

Enter the Spinal Cord at:

Dorsolateral Lissauer fasciculus

Ascend and Descend

Cross SC through ventral w.c. to:

contralateral ALS

Ascend through ALS to reticular formation,thalamus

8/13/2019 Physio CNS 2006

14/21

Axonal Pain Reflex

P

P

P

P Rubor- Red from enlarged

arterioles (oxygenated

blood)

DolorNociceptionTumorSwelling from

extravasated fluid

Type C

(Also bradykinin)

8/13/2019 Physio CNS 2006

15/21

Basal Ganglia Disturbances Parkinsonism

Degradation of DAergic neurons in SN Tremor, akinesia, bradykinesia,

cogwheel rigidity

Huntingtons Chorea

Loss of intrastriatal med. SpinyGABAergics (caudate atrophy)

Chorea, dementia, deceased tone

Ballism Damage to STN (corpus luysii) -

unilateral- hemiballismus

Flailing movements

Athetosis

Damage to GP and Putamen

Wormlike, writhing movements,

dystonia (posture issues) Tardive Dyskinesia

Iatrogenic side effect of neuroleptics(thorazine)

Involuntary mouth movements due tosupersensitivity of DA receptors

8/13/2019 Physio CNS 2006

16/21

Cerebellum

Architecture (covered before) Remember that climbing fibers

from inferior olivary nucleicause complex purkinje spikes,

Mossy fibers from other nucleicause simple spikes in purkinje

cells. Divisions

Cerebrocerebellum

Spinocerebellum

Vestibulocerebellum

Deep nuclei (send out

transmissions) Fastigial, Interposed

(globose,emboliform), Dentate,Lateral Vestibular Nucleus

Granule Cells are the onlyexcitatory ones!Parallel fibers

Cerebellar Lesions May Cause:

1. Motor Delay

2. Dysmetria (inaccuracy)

3. Dysdiadochokinesia

(alternating movement

disorders)

4. Intention Tremor, Ataxia, andApraxia

8/13/2019 Physio CNS 2006

17/21

Decorticate and Decerebrate

Postures

Decorticate: CNS Damage above level of

Red Nucleus

Rubrospinal Tract active- activates arm

flexors with response to pain or head turn incontralateral direction

Decerebrate: CNS Damage at or below

level of Red Nucleus Everything extended except fingers.

8/13/2019 Physio CNS 2006

18/21

The Human Retina

Light changes 11-cisretinal to: All-transretinal

This activates:

Transducin This activates

Phosphodiesterase

This changes:

cGMP to GMP

This causes: Cation channels to close - hyperpolarization

8/13/2019 Physio CNS 2006

19/21

Sleep Stages

REM-

Sawtooth waves, mixed frequency EEG

Dreaming, Paralysis

NREM-

Stage 1Low voltage, mixed freq

Stage 2Sleep spindles, K complexes

Stage 3Delta waves

Stage 4More Delta waves

8/13/2019 Physio CNS 2006

20/21

Reticular Formation

Raphe Nuclei Serotonin

SN, Ventral Tegmental Area

Dopamine

Nigrostriatal pathwayMotor Control

VTA-frontal cortex and VTA-nucleus accumbens

Dopaminergic neurons overactive in schizophrenia

Also important in reward effects of food, water, and drug

abuse

Locus Ceruleus:

Noradrenergic neurons control arousal and sleep-

wake cycle

8/13/2019 Physio CNS 2006

21/21

Learning and Memory

AMPA vs. NMDA

AMPA Glu receptors

are active during low-

frequency stimulation

Na+ channels

NMDA channels

require previous

depolarization through

AMPA channels, allow

Ca++ in.

http://store4.yimg.com/I/bronzedirect_1719_17282