NTA Level 4 • Semester 1 • PST04103

Structures and Functions of the Central Nervous System

Human Anatomy and Physiology • Source Session/Topic 34

Full source-text version: all educational wording from the extracted learning source is retained; only presenter/tutor metadata and web-layout noise are removed, while formatting is improved for readability.

Session 34: Structures and Functions of the Central Nervous System

Total Session Time: 120 minutes

Prerequisites

• None

Learning Tasks

By the end of this session students are expected to be able to:

• Define the Nervous system, Autonomic Nervous system, Somatic nervous

system, and Nerves

• List Components of the Nervous System

• Explain the Structure of Central Nervous System.

• State Functions of Nervous System

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board, chalk and whiteboard markers

• Overhead projector (OHP) and computer

• Handout 34.1:Synapse and synaptic transmission

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing

STEP 2: Definition and Components of the Nervous System (20minutes)

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|What is the nervous system autonomic nervous system? |

|What is somatic nervous system, and nerves? |

|What are the components of the nervous system? |

| |

|ALLOW few students to respond |

| |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

Nervous System

• Refers to the part of the body that coordinates its voluntary and

involuntary actions and transmits signals between different parts

• It is the system that conducts stimuli from sensory receptors to the

brain and spinal cord and that conducts impulses back to other parts of

the body.

Autonomic Nervous System

• The part of the nervous system that regulates the involuntary activity of

the heart, intestines, and glands, including digestion, respiration,

perspiration, metabolism, and blood-pressure modulation.

Somatic Nervous System

• The part of the peripheral nervous system that transmits signals from the

central nervous system to skeletal muscle and from receptors of external

stimuli, thereby mediating sight, hearing and touch.

Nerves

• Nerves are bundles of axons in the peripheral nervous system (PNS) that

act as information highways to carry signals between the brain and spinal

cord and the rest of the body.

Components of the nervous system:

• The Central Nervous System

o Brain

o Spinal cord

• Peripheral Nervous system is divided into:

o Autonomic nervous system

o Peripheral nervous system

STEP 3: Nerve Tissue (20 minutes)

|Activity: Small Group Discussion ( 30 minutes) |

| |

|DIVIDE students into small manageable groups |

| |

|ASK students to discuss on the following question |

|What are the parts of neuron? |

| |

|ALLOW students to discuss for 15 minutes |

| |

|ALLOW few groups to present and the rest to add points not mentioned |

| |

|CLARIFY and SUMMARIZE by using the contents below |

• Nerve tissue is made up of nerve cells called neurons or nerve fibers

• All neurons have the same physical parts.

o The cell body contains the nucleus and is essential for the continued

life of the neuron.

o Dendrites are processes (extensions) that transmit impulses toward the

cell body.

o The one axon of a neuron transmits impulses away from the cell body.

o It is the cell membrane of the dendrites, cell body, and axon that

carries the electrical nerve impulse.

o Axons and dendrites are collectively called Schwann cells in the

peripheral nervous system and are covered by a membrane called myelin

sheath.

o Node of Ranvier is the spaces between adjacent Schwann cells or

segments of myelin sheath.

o Neurolema are the nuclei and cytoplasm of Schwann cells.

• Synapse.

o It is the small gap or space between the axon of one neuron and the

dendrites/cell body of the next neuron.

o The synaptic knob of presynaptic axon contains chemical

neurotransmitters that are released to the synapse on the arrival of

an impulse.

o Synapses ensure one way impulse transmission

o The neurotransmitter diffuses across the synapse, combines with

specific receptor sites on the cell membrane of the postsynaptic

neuron, and there generates an electrical impulse that is, in turn,

carried by this neuron’s axon to the next synapse.

o Example of neurotransmitter is acetylcholine found at the

neuromuscular junction.

• Types of neurons

o Neurons are classified in to three groups which are :

▪ sensory (afferent) neuron,

▪ motor (efferent) neuron

▪ Interneuron.

o Sensory neurons

▪ Carry impulses from receptors to the central nervous system.

▪ Receptors detect external or internal changes and send the

information to the CNS in the form of impulses by way of the

afferent neurons.

▪ The central nervous system interprets these impulses as a

sensation.

o Motor neurons

▪ Carry impulses from the central nervous system to effectors.

▪ The two types of effectors are muscles and glands.

▪ In response to impulses, muscles contract or relax and glands

secrete.

o Interneurons

▪ They are found entirely within the central nervous system.

▪ They are arranged so as to carry only sensory or motor impulses,

or to integrate these functions.

▪ Some interneurons in the brain are concerned with thinking,

learning, and memory.

[pic]

Source: Scanlon,V.C. & Sandors, T (2007). Figure 34.1: Structures of

sensory and motor neuron

[pic][pic]Refer students to Handout 34.1: Synapse and synaptic

transmission

STEP 4: Central Nervous System (35 minutes)

|Activity: Small Group Discussion ( 30 minutes) |

| |

|DIVIDE students into small manageable groups |

| |

|ASK students to discuss on the following question |

|What are the main parts of central nervous system? |

| |

|ALLOW students to discuss for 15 minutes |

| |

|ALLOW few groups to present and the rest to add points not mentioned |

| |

|CLARIFY and SUMMARIZE by using the contents below |

• Central nervous system (CNS) is a part of nervous system which is made up

of brain and spinal cord

• The Spinal cord

o The spinal cord transmits impulses to and from the brain and is the

integrating centre for the spinal cord reflexes

o The spinal cord extends from the foramen magnum of the occipital bone

to the disc between the first and second lumbar vertebrae.

o The internal grey matter is shaped like the letter H

o Grey matter consists of the cell bodies of motor neurons and

interneurons.

o The external white matter is made of myelinated axons and dendrites of

interneurons.

o Emerging from the spinal cord are spine nerves.

o Spinal cord reflexes are those that do not depend directly on the

brain, although the brain may inhibit or enhance them.

o A reflex arc is the pathway that nerve impulses travel when a reflex

is elicited, and there are five essential parts:

▪ Receptors-detect a change (the stimulus) and generate impulses.

▪ Sensory neurons-transmit impulses from receptors to the CNS.

▪ Central nervous system-contains one or more synapses.

▪ Motor neurons-transmit impulses from the CNS to the effector.

▪ Effector-performs its characteristic action.

• The Brain

o The major parts of the brain are the medulla, pons, and midbrain

(collectively called the brain stem), the cerebellum, the

hypothalamus, the thalamus and the cerebrum.

o Ventricles are cavities in the brain where the cerebrospinal fluid is

found.

o Medulla

▪ The medulla extends from the spinal cord to the pons and is

anterior to the cerebellum.

▪ It contains cardiac centre, vasomotor centre and respiratory

centre hence controls heart rate, diameter of blood vessels and

breathing respectively.

▪ Also there are reflex centres for coughing, sneezing, swallowing,

and vomiting.

o Pons

▪ They bulge anteriorly from the upper part of the medulla.

▪ Within the pons are two respiratory centres that work with those

in the medulla to produce a normal breathing rhythm.

o Midbrain

▪ The midbrain extends from the pons to the hypothalamus

▪ Visual and auditory reflexes are integrated to the midbrain.

o Cerebellum

▪ It is concerned with movements like coordination, regulation of

muscle tone, the appropriate trajectory and endpoint of movements,

and the maintenance of posture and equilibrium.

o Hypothalamus

▪ It is located superior to the pituitary gland and inferior to the

thalamus

▪ Their functions include:

▪ Production of antidiuretic hormone and oxytocin which are stored

in the posterior pituitary gland

▪ Regulation of releasing hormone

▪ Regulation of food intake

▪ Regulation of body temperature

▪ Integration of the functioning of autonomic nervous system

▪ Stimulation f visceral response during emotions

▪ Regulation of body rhythms like hormone secretion and sleep

cycles.

o Thalamus

▪ It is superior to the hypothalamus and inferior to the cerebrum.

▪ Many of the functions of the thalamus are concerned with

sensation.

o Cerebrum

▪ It is lined with grey matter on the surface called cerebral

cortex

▪ The cerebral cortex has folds which enable us to read, speak, do

long division, and write and other things done by human that

animals cannot do because they lack the folds.

▪ The cerebral cortex is divided in to lobes which are frontal

lobe, parietal lobe, temporal lobe, and occipital lobe.

▪ Within the frontal lobes are the motor areas that generate the

impulses for voluntary movement, like that of hands, face, mouth in

speaking and others.

▪ The general sensory areas in the parietal lobes receive impulses

from receptors in the skin and feel and interpret the cutaneous

sensations and also from stretch receptors in muscles for conscious

muscle sense.

▪ The olfactory areas in the temporal lobes receive impulses from

receptors in the nasal cavities for the sense of smell.

▪ The olfactory association area learns the meaning of odours such

as the smell of sour milk, or fire.

▪ Occipital lobe contains visual association areas which interpret

what has seen and enable the thinking cerebrum to use the

information.

o Basal ganglia

▪ These are paired masses of grey matter within the white matter of

the cerebral hemispheres

▪ Their functions are certain subconscious aspects of voluntary

movement, and they work with the cerebellum.

▪ The basal ganglia help regulate muscle tone, and they coordinate

accessory movements such as swinging the arms when walking or

gesturing while speaking.

o Corpus collosum

▪ It connects the brain hemispheres to know what is going on to

each other.

▪ This is especially important for people because for most of us,

the left hemisphere contains speech areas and the right hemisphere

does not.

o Meninges

▪ These are connective tissue that covers the brain and the spinal

cord.

▪ Between the membranes of meninges there is cerebrospinal fluid,

the tissue fluid of the central nervous system.

▪ Examination of the fluid can be used to diagnose certain

diseases.

o Cranial nerves

▪ These are nerves which emerge from the brain stem or other parts

of the brain and are about twelve.

▪ They carry impulses for functions involving the head.

▪ The impulses for the senses of smell, taste, sight, hearing, and

equilibrium are all carried by cranial nerves to their respective

sensory areas in the brain.

[pic]

Source: Scanlon,V.C . & Sandors,T (2007). Figure 34.2: The brain as

seen from left side

STEP 6: Functions of the Nervous System (30 minutes)

• The nervous system has 3 main functions;

o Sensory

o Integration, and

o Motor.

Sensory

• The sensory function of the nervous system involves collecting

information from sensory receptors that monitor the body’s internal and

external conditions.

• These signals are then passed on to the central nervous system (CNS)

for further processing by afferent neurons (and nerves).

Integration

• The process of integration is the processing of the many sensory

signals that are passed into the CNS at any given time.

• These signals are evaluated, compared, used for decision making,

discarded or committed to memory as deemed appropriate.

• Integration takes place in the grey matter of the brain and spinal cord

and is performed by interneurons.

• Many interneurons work together to form complex networks that provide

this processing power.

Motor

• Once the networks of interneurons in the CNS evaluate sensory

information and decide on an action, they stimulate efferent neurons.

• Efferent neurons (also called motor neurons) carry signals from the

grey matter of the CNS through the nerves of the peripheral nervous

system to effector cells.

• The effector may be smooth, cardiac, or skeletal muscle tissue or

glandular tissue.

• The effector then releases a hormone or moves a part of the body to

respond to the stimulus

STEP 6: Key Points (5 minutes)

• The nervous system is one of the regulating systems by which

electrochemical impulses make it possible to obtain information about the

external or internal environment

• Neurons are classified in to three groups which are sensory (afferent)

neuron, motor (efferent) neuron and interneuron.

• Central nervous system is a part of nervous system which is made up of

brain and spinal cord.

STEP 7: Evaluation (5 minutes)

• What is nervous system?

• What are the components of nervous system?

• What are the functions of nervous system?

• What are the parts of a neuron?

References

Seeley, R. R., Stephens, T. D., &Tate, P. (2003). Anatomy and Physiology.

New York:

McGraw-Hill.

Shier, A., Butler, J., & Lewis, R. (2004). Hole’s Human Anatomy &

Physiology. New York:

McGraw-Hill.

Standring, S. (2008). Grays’s Anatomy The anatomical basis of clinical

practice. United

Kingdom: Churchill Livingstone Elservier.

Thibodeau, G. A., & Patton, K. T. (1999). Anatomy & Physiology. Saint

Louis: Mosby, Von

Hoffman Press, Inc.

Waugh, A., & Grant, A. (2006). Ross and Willson Anatomy and physiology in

Health and

illness. United Kingdom: Churchill Livingstone Elservier.

|[pic] |Handout 34.1: Synapse and synaptic transmission |

• The neurotransmitter diffuses across the synapse, combines with

specific receptor sites on the cell membrane of the postsynaptic

neuron, and there generates an electrical impulse that is, in turn,

carried by this neuron’s axon to the next synapse, and so forth.

• A chemical inactivator at the cell body or dendrite of the

postsynaptic neuron quickly inactivates the neurotransmitter.

• This prevents unwanted, continuous impulses, unless a new impulse from

the first neuron releases more neurotransmitter.

• Many synapses are termed excitatory, because the neurotransmitter

causes the postsynaptic neuron to depolarize (become more negative

outside as Na+ ions enter the cell) and transmit an electrical impulse

to another neuron, muscle cell, or gland.

• Some synapses, however, are inhibitory, meaning that the

neurotransmitter causes the postsynaptic neuron to hyperpolarize

(become even more positive outside as K+ions leave the cell or Cl-

ions enter the cell) and therefore not transmit an electrical impulse.

• Such inhibitory synapses are important, for example, for slowing the

heart rate, and for balancing the excitatory impulses transmitted to

skeletal muscles.

• With respect to the skeletal muscles, this inhibition prevents

excessive contraction and is important for coordination.

• An example of a neurotransmitter is acetylcholine, which is found at

neuromuscular junctions, in the CNS, and in much of the peripheral

nervous system.

• Acetylcholine usually makes a postsynaptic membrane more permeable to

Na+ ions, which brings about depolarization of the postsynaptic

neuron.

• Cholinesterase is the inactivator of acetylcholine.

• There are many other neurotransmitters, especially in the central

nervous system.

• These include dopamine, GABA, norepinephrine, glutamate, and

serotonin.

• Each of these neurotransmitters has its own chemical inactivator.

• Some neurotransmitters are reabsorbed into the neurons that secreted

them; this process is called reuptake and also terminates the effect

of the transmitter.

[pic]

Source: Scanlon,V.C. & Sandors,T (2007). Figure 34.3: Impulse

transmission at a synapse

← Previous Topic Next Topic →View all Human Anatomy and Physiology topics Open Complete Full Notes

PDF / OFFLINE NOTES

Unataka kutumiwa notes hizi kupitia WhatsApp?Kwa notes zilizopangiliwa vizuri kwa kusoma offline au PDF, bonyeza kitufe hapa chini. Ujumbe wenye Level, Semester, Module na Topic utaandaliwa moja kwa moja.TUMIWA NOTES WHATSAPP

WhatsApp: 255620339260