nervous system · 2017-02-16 · histology of the nervous system o session 16 (lectures 29 and 30)...

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BIOH111

oCell Module

oTissue Module

o Integumentary system

oSkeletal system

oMuscle system

oNervous system

oEndocrine system


Textbook and required/recommended

readings

o Spinal cord anatomy: Principles of anatomy and physiology.

Tortora et al; 14th edition: Chapter 13; section 13.1

o Spinal cord physiology: Principles of anatomy and physiology.

Tortora et al; 14th edition: Chapter 13; section 13.3


BIOH111 – NERVOUS SYSTEM MODULEo Session 15 (Lectures 27 and 28) – Organisation and

histology of the nervous system

o Session 16 (Lectures 29 and 30) – Function of neurons:

conduction of nerve impulses

o Session 17 (Lectures 31 and 32) – CNS: Brain anatomy

and function

o Session 18 (Lectures 33 and 34) – Sensations and special

senses

o Session 19 (Lectures 35 and 36) – Spinal cord anatomy

and physiology

o Session 20 (Lectures 37 and 38) – Spinal nerves and

somatic sensory and motor pathways

o Session 21 (Lectures 39 and 40) – Autonomic nervous

system: anatomy and function

BIOH111

Lectures 35 and 36

Spinal cord anatomy and physiology

Department of Bioscience

endeavour.edu.au


Objectives

Lecture 35:

Anatomy and function of spinal cord:

Describe structure and functions of spinal cord, including supporting system

Describe external and internal anatomy of spinal cord

Describe and discuss arrangement and functions of grey and white matter in

the spinal cord

Lecture 36:

Describe and understand reflex arcs

Describe and understand ascending and descending tracts

Understand the relationship between functions of the spinal cord grey and

white matter in conducting nerve impulses


FUNCTIONS OF SPINAL CORDo The spinal cord and spinal nerves mediate reactions to

environmental changes.

1. Processes reflexes

2. Site for integration of EPSPs and IPSPs that arise locally

or are triggered by nerve impulses from the periphery and

brain.

3. Conduction pathway for sensory and motor nerve

impulses.


NERVOUS SYSTEM DIVISIONS - REVISION


SPINAL CORD SUPPORT SYSTEMS

o The spinal cord is protected and supported by:

1. Vertebral column: provides a bony covering and support

of the spinal cord (revision: BIOH111 session 8)

2. Meninges: connective tissue covering

3. Cerebrospinal fluid

RE

VIS

ION


MENINGES

o 3 coverings that run

continuously around the spinal

cord and brain:

1. Dura mater: outer layer; dense

irregular tissue

2. Arachnoids: middle layer; spider

web of collagen fibers

3. Pia mater: inner meninx; thin,

transparent connective tissue layer

that adheres to the surface of the

spinal cord and brain


CEREBROSPINAL FLUID (CSF) - revision

o Cerebrospinal fluid (CSF) is a clear, colorless liquid that protects the spinal cord and brain against chemical and physical injuries.

o Structure: Clear liquid containing glucose, proteins, & ions; 80-150 ml; produced by ependymal cells; production rate same as reabsorption rate (20ml/hour); contained within Subarachnoid space

o Functions:

1. mechanical protection: floats cord & softens impact with bony walls

2. chemical protection: optimal ionic concentrations for action potentials

3. circulation: nutrients and waste products to and from bloodstream

o Clinical applications: meningitis and spinal tap


EPENDYMAL CELLS - revision

o Structure: columnar cells

with apical cilia

o Functions:

• form epithelial membrane

lining cerebral cavities &

central canal

• produce cerebrospinal

fluid (CSF)

synapticplasticity.wix.com

http://synapticplasticity.wix.com/sp#!gallery


EXTERNAL ANATOMY OF THE

SPINAL CORD

o Flattened cylinder; 16-18 Inches long & 3/4

inch diameter

o In adult ends at L2; in newborn ends at L4;

growth of cord stops at age 5

o Begins as a continuation of medulla

oblongata and terminates at about the

second lumbar vertebra in an adult;

segmented into spinal segments - origin

points for spinal nerves

o Cervical and lumbar enlargements: serve as

points of origin for nerves to the extremities

o Conus medullaris: tapered portion of the

spinal cord; spinal tap area below conus

medullaris


INTERNAL ANATOMY OF THE

SPINAL CORD – SPINAL SEGMENT

o General structure: gray matter shaped like the letter H or a

butterfly surrounded by the white matter

o Anterior median fissure and the posterior median sulcus divide

spinal cord into right and left sides.

anterior median fissure

posterior median sulcus

white matter gray matter


GRAY MATTER OF THE SPINAL CORD

o Structure:

• paired dorsal and ventral gray

horns

• lateral horns only present in

thoracic spinal cord

• gray commissure surrounds central

canal

• nuclei and unmyelinated axons of

association and motor neurons

o Function: receives and integrates

incoming and outgoing

information; reflex arcs

central canal

dorsal gray horns

ventral gray horns


Objectives

Lecture 35:

Anatomy and function of spinal cord:

Describe structure and functions of spinal cord, including supporting system

Describe external and internal anatomy of spinal cord

Describe and discuss arrangement and functions of grey and white matter in

the spinal cord

Lecture 36:

Describe and understand reflex arcs

Describe and understand ascending and descending tracts

Understand the relationship between functions of the spinal cord grey and

white matter in conducting nerve impulses


REFLEXES AND REFLEX ARCS

o Reflex: fast, predictable, automatic response to

changes in the environment that helps to maintain

homeostasis; 4 types:

1. Spinal – integration occurs in spinal grey matter; e.g.

patellar reflex

2. Cranial – integration occurs in brain stem; e.g. eye

movement while reading

3. Somatic – involves contraction of skeletal muscles

4. Autonomic – not consciously perceived; e.g. heart rate

o Reflex arc: specific nerve impulse pathway that

produces a reflex; include at least one synapse


12

3 4 5

REFLEX ARCo 5 components:

1. Sensory receptor – responds to stimulus

2. Sensory neuron – conducts nerve impulse from receptor to integrating

center

3. Integrating center – CNS region(s) relay impulses from sensory to

motor neurons (EPSPs and IPSPs)

4. Motor neuron - conducts nerve impulse from integrating center to

effector (EPSPs and IPSPs)

5. Effector – responds to stimulus

(EPSPs and IPSPs)

o Somatic spinal reflexes: stretch reflex, tendon reflex, flexor

(withdrawal) reflex, and crossed extensor reflex; all exhibit

reciprocal innervation.


Stretch (Patellar) ReflexSignal Reflex arc type Reciprocal

innervation

Effect Function

muscle spindle

signals stretch of

muscle

Monosynaptic,

ipsilateral

Polysynaptic;

interneuron

antagonistic

muscles relax as

part of reflex

motor neuron

activated & muscle

contracts

Feedback

mechanism to

control muscle

length by causing

muscle contraction


Tendon ReflexSignal Reflex arc type Reciprocal

innervation

Effect Function

stretching of tendon Polysynaptic

ipsilateral

Polysynaptic;

interneuron

contraction of

ipsilateral muscle

group

Inhibitory neuron is

stimulated;

motor neuron is

hyperpolarized and

muscle relaxes

feedback

mechanism to

control muscle

tension by causing

muscle relaxation

when muscle force

becomes too

extreme


Flexor (Withdrawal) ReflexSignal pain

Reflex arc

type

Intersegmental; Ipsilateral

Reciprocal

innervation

Polysynaptic; interneuron

contraction of ipsilateral

muscle group

Effect - Interneurons branch to

different spinal cord

segments

- Motor fibers in several

segments are activated

- More than one muscle

group activated to lift foot

off away from pain

Function protective withdrawal reflex

that moves a limb to avoid

pain

Not assessable


Crossed Extensor Reflex

Signal pain

Reflex arc

type

Intersegmental;

contralateral

Reciprocal

innervation

Polysynaptic; extensors

contract flexors relax

Effect Contralateral extensor

muscles are stimulated by

interneurons to hold up the

body weight

Function protective withdrawal reflex

that moves a limb to avoid

pain

Not assessable


WHITE MATTER OF THE SPINAL CORDo Structure:

• White matter is divided into columns:

distinct bundles of myelinated axons

of motor and sensory neurons that

have a common origin, destination

and function; 3 pairs: dorsal, lateral

and anterior

• Bundles in columns are called tracts;

2 types: ascending and descending

o Function: tracts are highways for

nerve impulse conduction to and

from the brain

Dorsal columns

Lateral columns

Anterior columns


SENSORY AND MOTOR TRACTS

o Sensory (ascending) tracts conduct nerve impulses toward

the brain.

• lateral and anterior spinothalamic tracts and posterior column tract

o Motor (descending) tracts conduct impulses down the cord.

• Direct pathways: lateral and anterior corticospinal and corticobulbar

tracts

• Indirect pathways: rubrospinal, tectospinal, and vestibulospinal tracts

↑ sensory (ascending) tracts

↓ motor (descending) tracts


Naming of tracts

• indicates position & direction of signal

• Example: anterior spinothalamic tract

– impulses travel from spinal cord towards brain

(thalamus)

– found in anterior part of spinal cord

• Example: anterior corticospinal tract

– impulses travel from___ towards___

– found in WHAT part of the spinal cord


Babinski sign

o Checking a patient’s reflexes may help to detect

disorders/injury

o Plantar flexion reflex -- stroke the lateral margin of the

sole

• normal response is curling under the toes

• abnormal response or response of children under 18

months is called Babinski sign (upward fanning of

toes due to incomplete myelination in child)

Clinical application:


Work in groups of 2-4: follow the neurons

below and comment on the structures

encountered and integrate functions between

grey and white matter in spinal cord and brain

with sensation and effect.


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nervous system · 2017-02-16 · histology of the nervous system o session 16 (lectures 29 and 30)...

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