HLT31507 CERTIFICATE III IN NUTRITION & DIETETIC ASSISTANCE

THE NERVOUS SYSTEMdelivered by:

Mary-Louise Dieckmann

Functions of the Nervous System

• Sensory Input• Integration• Motor Output

Sensory Input

• Gathering information• To monitor changes occurring inside and outside

the body

• Changes = stimuli

Integration• To process and interpret sensory input and decide if action is needed

Motor Output

• A response to integrated stimuli• The response activates muscles or

glands

Structural Classification• Central nervous system (CNS)– Brain– Spinal cord

• Peripheral nervous system (PNS)– Nerve outside the brain and spinal cord

Organisation of the Nervous System

Functional Classification• Sensory (afferent) division– Nerve fibers that carry information to the central nervous system

• Motor (efferent) division– Nerve fibers that carry impulses away from the central nervous system

Functional Classification• Motor (efferent) division– Two subdivisions• Somatic nervous system = voluntary• Autonomic nervous system = involuntary – consists of sympathetic and parasympathetic, both systems work together – dynamic balance.

Sympathetic Division

• ‘fight or flight system.’• Increases HR, BP, blood glucose levels, dilates

bronchioles of lungs, allows individual to cope with stress.

• Dilates blood vessels, diverts blood away from digestive organs.

• Enables body to cope rapidly and vigorously with situations that threaten homeostasis.

• E= exercise, excitement, emergency and embarrassment.

Parasympathetic Division• Resting and digesting system • Most active when body is at rest.• Promotes normal elimination, conserves body energy, decreases demands on the cardiovascular system.• BP and HR are decreased, helps digest food, keeps skin warm and pupils constricted.• D = Digesting, defecation, diuresis (urinating)

Nervous Tissue• Neurons = nerve cells– Cells specialized to transmit messages– Major regions of neurons• Cell body – nucleus and metabolic center of the cell• Processes – fibers that extend from the cell body

Nervous Tissue

Myelin• Most long nerve fibers or axons are covered in a white fatty substance called the myelin sheath.• This sheath protects, insulates and increases the speed of nerve impulses.• Myelin give the brain its white colour. Without myelin the affected person loses control of their muscles (M.S.)• White matter – dense collections of myelinated fibers. Grey matter – mostly unmyelinated fibers.

Myelin

Nervous Tissue• Extensions outside the cell body– Dendrites – conduct impulses toward the cell body– Axons – conduct impulses away from the cell body

Synapses• Anatomically neurons do not touch or join up with each other.• Each neurons axonial terminal is separated from the next neuron by a tiny gap called a synaptic cleft.• Synaptic cleft is crossed by a neurotransmitter (chemical messenger)• Action of neurotransmitter is shortlived – once they have stimulated the next neuron they are neutralised by enzymes.

Functional Classification of Neurons

• Sensory (afferent) neurons– Carry impulses from the sensory receptors• Cutaneous sense organs

• Motor (efferent) neurons– Carry impulses from the central nervous system

Neuron Classification

Functional Properties of Neurons

• Irritability – ability to respond to stimuli• Conductivity – ability to transmit an impulse• The plasma membrane at rest is polarized– Fewer positive ions are inside the cell than outside

the cell

Continuation of the Nerve Impulse

• Impulses are able to cross the synapse to another nerve– Neurotransmitter is released from a nerve’s axon terminal– The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter– An action potential is started in the dendrite

How Neurons Communicate at Synapses

Central Nervous SystemThe brain looks like two fistfuls of pinkish grey tissue – wrinkled like a walnut, weighs about 1600 grams (approx. 3 pounds)Principal parts include• 1. The brain stem – includes medulla oblongata, pons and midbrain• 2. Diencephalon – includes thalamus and hypothalamus• 3. Cerebrum• 4. Cerebellum

CNS continued• The brain is protected by cranial bones, meninges (membranes and cerebospinal fluid (CSF).• Fluid circulates through membrane spaces and in cavities within brain and spinal cord. Protects and helps in exchange of nutrients and waste products.• Brain only 2% of body weight but consumes about 20% of oxygen.

Anatomical structures of CNS• Brain Stem – about the size of a thumb in diameter and approx 3 inches long• Medulla oblongata – most inferior part of brain stem – merges into spinal cord. Pathway for ascending (sensory) and descending (motor) tracts. Plays a crucial role in maintaining some vital activities.

Role of Medulla Oblongata • Controls force and rate of heat• Regulates BP by acting on smooth muscle in walls of blood vessels (constriction cause BP to increase and dilation cause BP to decrease)• Controls rate and depth of breathing• Regulates activities such as vomiting, swallowing, coughing and sneezing. If this part is injured what might happen?

Anatomical structures of CNS cont.

• Pons – means bridge, - rounded structure protrudes just below midbrain. Connects spinal cord to brain. Helps in control of breathing.• Midbrain – small part of brain stem. Contains ascending sensory and descending motor tracts. Contains reflex center for head in response to auditory stimuli (eg. startle reflex – turn your head towards an unexpected sound). Reflex centre for head and eye movements (watching a tennis game)

CNS anatomy cont.• Thalamus – egg shaped – means “inner room”. Plays a key role in mediating sensation, motor activities and memory. Sorts out and edits information. Relay station for sensory impulses. Gateway to cerebral cortex.• Hypothalamus – positioned below thalamus. Important autonomic nervous system center. Regulates body temperature, water balance and metabolism• Center for emotions – perceives thirst, hunger, pain, sex drive.

CNS anatomy cont.• Cerebrum – forms most superior part of brain, looks like a mushroom cap. Is marked by deep fissures/folds. Deep grooves are fissues, shallow grooves are sulci and gyri are elevated ridges.• Lobes – frontal, parietal, temporal, occipital are named after cranial bones – are separated by sulci.

Functions of Lobes• Parietal lobe is the sensory area – allows you to recognise pain, cold and touch• Frontal Lobe is motor area – allows us to move our muscles• Frontal Lobe also has an association area – allows us to use higher intellectual and psychic functions.

CNS anatomy cont.• Cerebellum – large cauliflower like projection from under occipital lobe• Provides subconscious (not aware) timing for skeletal muscle activity.• Helps us with balance, posture• Co-ordinates complex sequences of skeletal muscle contractions.

Protection of CNS

• Meninges– Dura mater (outermost layer)– Arachnoid mater (middle later)– Pia mater (innermost membrane)

CSF – Cerebrospinal fluid

Protection of CNS• Blood brain barrier – least permeable capillaries in entire body – only allows water soluable substances in such as water, glucose and essential amino acids to pass through walls into CNS. However cannot stop fats, respiratory gases and fat soluable molecules – thus alcohol, nicotine and anesthetics can affect the brain

Traumatic Brain Injuries• Concussion– Slight brain injury– No permanent brain damage

• Contusion– Nervous tissue destruction occurs– Nervous tissue does not regenerate

• Cerebral edema– Swelling from the inflammatory response– May compress and kill brain tissue

Cerebrovascular Accident (CVA)

• Commonly called a stroke• The result of a ruptured blood vessel supplying a region of the brain• Brain tissue supplied with oxygen from that blood source dies• Loss of some functions or death may result

Alzheimer’s Disease

• Progressive degenerative brain disease• Mostly seen in the elderly, but may begin in

middle age• Structural changes in the brain include

abnormal protein deposits and twisted fibers within neurons

• Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death

Spinal Cord

• Extends from the medulla oblongata to the region of T12

• Below T12 is the cauda equina (a collection of spinal nerves)

• Enlargements occur in the cervical and lumbar regions

Figure 7.18

Examples of Nerve Distribution

Figure 7.23

Autonomic Nervous System

Comparison between Sympathetic & Parasympathetic Division