CH 4 NERVOUS SYSTEM IS HIGHLY ORGANISED

Question 1

2 divisions of NS

Answer 1

CNS - brain, spinal cord

PNS - nerves that connect CNS with receptors, muscles and glands

Question 2

which structures protect the CNS?

Answer 2

• bone
• membranes called meninges
• cerebrospinal fluid

Question 3

describe structure/location of cranium and vertebrae

Answer 3

• brain protected by cranium, part of skull that houses brain
• spinal cord runs through vertebral canal, an opening in the vertebrae
• these bones provide a strong, rigid structure to protect structures underneath

Question 4

describe the 3 meningeal layers

Answer 4

connective tissue forming membranes called meninges

• outer; dura mater; tough and fibrous - layer of protection. sticks closely to bones of the skull, but on inside of vertebral canal it is not close to fitting. texture and thickness similar to a household rubber glove
• middle; arachnoid mater; loose mesh of fibres
• inner; pia mater; far more delicate. contains many blood vessels, sticks closely to surface of brain and spinal cord.

Question 5

what is cerebrospinal fluid? name its 3 functions.

Answer 5

clear, watery fluid containing a few cells and some glucose, protein, urea, salts. occupies a space between middle and inner meningeal layers, circulates through cavities in brain & through a canal in spinal cord.

• protection: shock absorber cushions blows
• support: brain suspended in cranium
• transport: CSF formed in blood and circulates around through CNS before re-entering blood capillaries. during circulation, it takes nutrients to the cells of the brain and carries away their waste

Question 6

name 5 main structures of the brain

Answer 6

• corpus callosum
• cerebrum
• hypothalamus
• medulla oblongata
• cerebellum

Question 7

describe the main features of the cerebrum

Answer 7

biggest part of the brain consists of;

• cerebral cortex
• a deeper layer of white matter
• additional grey matter centre, the basal ganglia.

Question 8

describe the structure of the cerebral cortex

Answer 8

• outer grey matter layer consists of neuron cell bodies, dendrites, unmyelinated axons.
• folded in patterns, greatly increasing surface area (contains 70% of all neurons in CNS).
• folding produces convolutions (gyri) which are separated by either shallow downfolds (sulci) or deep downfolds (fissures)

Question 9

what does the longitudinal fissure do?

Answer 9

almost separates the cerebrum into two halves - left and right cerebral hemispheres
- joining the two at the base of the fissure is an area of white matter consisting of a large bundle of traverse fibres; corpus callosum

Question 10

why is grey matter grey and white matter white?

Answer 10

the fatty nature of myelin gives the white matter its colour and texture. because grey matter contains unmyelinated axons, it doesn’t posses the same pigment, and is therefore grey

Question 11

name the 5 lobes of the brain and briefly state their functions

Answer 11

frontal lobe: thinking problem solving, emotions, personality, language, control of movement
parietal lobe: processing temperature, touch, taste, pain and movement
temporal lobe: processing memories and linking them with senses; receives auditory information
occipital lobe: vision
insula: recognition of different senses and emotions, addiction and psychiatric disorders (deep inside the brain)

Question 12

identify the functions of the cerebral cortex

Answer 12

involved with thinking, reasoning, learning, memory, intelligence, sense of responsibility.
perception of the senses and initiation and control of voluntary muscle contraction

Question 13

name the three main functional areas in which the cerebra cortex can be divided

Answer 13

sensory areas: interpret impulses from receptors
motor areas: send impulses to muscles for control muscular movements
association areas: concerned with intellectual and emotional processes

Question 14

what physically happens when a memory is stored

Answer 14

memories are not stores in single cells. they are pathways of nerve cells. new links are made between neurons or existing links are modified.

Question 15

usually, what sorts of specialised functions are controlled by the right and left hemispheres?

Answer 15

left: language ability, voluntary movement on right side of the body
right: musical and artistic abilities, voluntary movement on left side of the body

Question 16

what are tracts and where do they occur

Answer 16

within the CNS bundles of nerve fibres are called tracts. outside the CNS bundles of nerve fibres are called nerves
3 types occur in the white matter;
- tracts that connect various areas of the cortex within the same hemisphere
- tracts that carry impulses between the left and right hemispheres
- tracts that connect the cortex to the other parts of the brain or to the spinal cord

Question 17

briefly explain the structure and function of the basal ganglia

Answer 17

• consists of groups of nerve cell bodies associated with control of skeletal muscles
• which play a role in initiating desired movements and inhibiting unwanted movements

Question 18

what is the function of the corpus callosum?

Answer 18

• wide band of nerve fibres lies underneath cerebrum at base of longitudinal fissures
• nerve fibres in the corpus callosum cross from one cerebral hemisphere to the other and allow the two halves to communicate with each other

Question 19

physically describe the cerebrum

Answer 19

• second largest part of the brain
• surface folded into a series of parallel ridges
• lies under the rear part of the cerebrum
• outer folded part is grey matter
• inside is white matter that branches to all parts of the cerebellum

Question 20

what is the function of the cerebellum?

Answer 20

• control over posture, balance, fine coordination of voluntary muscle movement. to carry out these functions, the cerebellum must receive sensory info from:
• • the inner ear for info about posture and balance
• • stretch receptors in skeletal muscles for info about the length of muscles
• all functions are under unconscious control
• we can move without it but movements would be jerky and uncontrolled

Question 21

what are the functions of the hypothalamus?

Answer 21

• maintaining constant internal environment - homeostasis
  functions include regulation of:
• autonomic nervous system (including regulation of heart rate, blood pressure, secretion of digestive juices, movements of alimentary canal, diameter of pupil in the eye)
• body temp
• food and water intake
• patterns of waking and sleeping
• contraction of urinary bladder
• emotional responses, e.g. fear, anger, aggression, pleasure, contentment
• secretion of hormones and coordination of parts of the endocrine system; acting through pituitary gland, hypothalamus regulates metabolism, growth, reproduction, responses to stress

Question 22

what is the medulla oblongata and what are its functions?

Answer 22

• continuation of the spinal cord
• extends from point where spinal cord enters the skull
• many nerve fibres pass through medulla going to or from other parts of the brain
• important role in automatically adjusting body functions

Question 23

what are the 3 ‘centres’ contained in the medulla oblongata?

Answer 23

cardiac centre: regulates rate and force of the heartbeat
respiratory centres: control rate and depth of breathing
vasomotor centre: regulates diameter of blood vessels
- in addition, other centres regulate sneezing, coughing and vomiting. all these centres are controlled by higher centres in the brain, particularly the hypothalamus

Question 24

how is the spinal cord protected?

Answer 24

• enclosed in vertebral canal (3 meningeal layers)
• dura mater not joined to the bone; instead, a space containing fat connective tissue and blood vessels serves as padding and allows cord to bend when spine is bent

Question 25

talk about the structure of the spinal cord, in reference to a cross-sectional image

Answer 25

• grey matter in centre (letter H shape), surrounded by white matter
• in the cross bar of the h, a small space called the central canal runs through the length of the spinal cord and contains CSF
• myelinated fibres arranged in ascending and descending tracts
• ascending: sensory axons that carry impulses upwards, towards the brain
  descending: motor axons that conduct impulses downwards, away from the brain

Question 26

identify 2 functions of the spinal cord

Answer 26

• carry sensory impulses up to the brain, and motor impulses down and away from the brain
• integrate certain fast, automatic responses called reflexes

Question 27

what is the peripheral nervous system composed of?

Answer 27

• nerve fibres that carry impulses to and from the CNS

- ganglia which lie outside the brain and spinal cord

Question 28

what are cranial nerves?

Answer 28

12 pairs of nerves, e.g. optic nerves which arise from the brain

• most are mixed (send and receive)
• sensory fibres (receive)
• motor fibres (send)

Question 29

what does a dorsal root and ventral root have to do with spinal nerves?

Answer 29

• 31 pairs of spinal nerves arise from the spinal cord
• all mixed fibres
• each nerve is joined to the cord by a ventral root and a dorsal root
• ventral root contains axons of motor neurons that have their cell bodies in the grey matter of the spinal cord
• dorsal root contains the axons of sensory neurons that have their cell bodies in a small swelling on the root known as the dorsal root ganglia

Question 30

name the 2 top divisions of the PNS

Answer 30

• afferent

- efferent

Question 31

explain the afferent division

Answer 31

• aka sensory division
• has fibres that carry impulses into the CNS by sensory neurons from receptors in the skin and around muscles and joints. said neurons can be further divided into;
• • somatic sensory neurons: bring impulses from the skin and the muscles
• • visceral sensory neurons: which brings impulses from the internal organs

Question 32

explain the efferent division

Answer 32

• aka motor division
• has fibres that carry impulses away from CNS. subdivided into;
  
  • • somatic division: tasked impulses from CNS to skeletal muscles
  • • autonomic division: carries impulses from the CNS to heart muscle, involuntary muscles and glands. further subdivided into:
    • – sympathetic division
    • – parasympathetic division

Question 33

how does the autonomic nervous system function? what is its function?

Answer 33

• controls body’s internal environment and is involved in many of the mechanisms that keep it constant
• usually operates without conscious control & is regulated by medulla oblongata, hypothalamus + cerebral cortex
  some regulation functions include:
• heart rate
• blood pressure
• body temperature
• digestion
• release of energy
• pupil diameter
• air flow to the lungs
• defecation
• urination

Question 34

characteristics of the ANS

Answer 34

effectors: heart muscle, involuntary muscle, glands
general function: homeostasis in response to internal env.
efferent pathways: two nerve fibres from CNS to effector with a synapse in a ganglion
neurotransmitter at effector: acetylcholine or noradrenaline
control: usually involuntary
nerves at target organ: two sets - sympathetic + parasympathetic
effect on target organ: excitation or inhibition

Question 35

characteristics of the SNS

Answer 35

effectors: skeletal (voluntary muscles)
general function: response to external environment
efferent pathways: one nerve fibre from the CNS to effector, no synapse, no ganglion
neurotransmitter at effector: acetylcholine
control: usually voluntary
nerves at target organ: one set
effect on target organ: always excitation

Question 36

what can generally be said about the functions of the parasympathetic and sympathetic divisions

Answer 36

• parasympathetic generally produces responses that maintain the body during relatively quiet conditions {ACETYLCHOLINE released by nerve endings]
• sympathetic generally produces responses that prepare the body for strenuous activity [NORADRENALINE released by nerve endings]
• message from the autonomic nerves goes to muscles + glands under their control is carried by a neurotransmitter at nerve endings.

Question 37

effects of sympathetic stimulation

Answer 37

heart: increases rate and strength of contraction
lungs: dilates bronchioles (fine air passages in lungs)
stomach, intestines: decreases movement
liver: increases breakdown of glycogen and release of glucose
iris of eye: dilates pupil
sweat glands: increases sweat secretion
salivary glands: decreases saliva secretion
blood vessels of
–skin: constricts vessels
–skeletal muscle: dilates vessels
–internal organs: constricts vessels (except in heart and lung)
urinary bladder: relaxes muscle of wall
adrenal medulla: stimulates hormone secretion

Question 38

effects of parasympathetic stimulation

Answer 38

heart: decreases rate and strength of contraction
lungs: constricts bronchioles
stomach, intestines: increases movement
liver: increases uptake of glycogen and synthesis of glucose
iris of eye: constricts pupil
sweat glands: no effect
salivary glands: increases saliva secretion
blood vessels of
–skin: little effect
–skeletal muscle: no effect
–internal organs: little effect
urinary bladder: constricts muscle of wall
adrenal medulla: no effect

Question 39

what is meant by ‘fight or flight’?

Answer 39

• in threatening situations, balance is thrown off and sympathetic becomes dominant
• stress-inducing situations provoke fight or flight response
• prepare body for increased activity, relying on skeletal muscles to produce movement and an increased level of alertness to act quickly
• requires greater supply of oxygen and glucose and hence increased blood flow to relevant structures