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1

The two parts of the nervous system

Central Nervous System
- Brain and spinal cord
- Control centre

Peripheral Nervous System
- Nerve cells, receptors
- Carry messages to and from CNS

2

Functional Types of Neurons

1. Sensory
- carry messages from receptors in sense organs towards CNS

2. Motor
- Carry messages away from CNS

3. Interneuron
- Link between sensory and motor neurones in the CNS

3

Structural types of Neurons

1. Multipolar
2. Bipolar
3. Unipolar
4. Pesudounipolar

4

Conduction along myelinated fibres

In unmyelinated fibres, depolarisation of one area of the membrane causes another repolarization immediately next to the original stimulus

This process repeats along the whole membrane, moving away from the original stimulus, from one channel to the next

The nerve impulse is prevented from going backwards by the refractory period

5

Conduction along myelinated fibres

In myelinated fibres, the nerve fibres are insulated from the extracellular fluid by schwann cells
Ions cannot flow where the fibre is insulated so no action potential can occur, except at the nodes of ranvier

Sodium ions will diffuse along axon through the cytoplasm until they reach the next exposed gate (node of ranvier), the action potentials are said to jump from one node to another

With action potentials only occurring at the nodes of ranvier, there is less distance to cover = much faster
Conduction along a myelinated axon is also called saltatory conduction

6

Synapses

1. Nerve impulse reaches axon terminal which activates voltage-gated ion channels in presynaptic membrane

2. Calcium ions flow into the presynaptic axon terminal

3. This stimulates the release of chemicals called neurotransmitters from vesicles by exocytosis at the presynaptic membrane

4. The neurotransmitters diffuse across the synaptic cleft and attach to receptors on the postsynaptic membrane

5. This stimulates ligand-gated protein channels to open, which allows an influx of sodium ions into the dendrite, initiating a nerve impulse in the next neuron

7

Examples of Neurotransmitters

→ Acetylcholine → Noradrenaline → Dopamine → Histamine → Serotonin

8

Removal of Neurotransmitters

Diffusion
→ Neurotransmitters exit the synaptic cleft via diffusion as they move from a high to a lower concentration

Enzymes degradation
→ Enzymes can inactivate the neurotransmitter, these are released by the postsynaptic membrane when the neurotransmitter has been received

Active reabsorption
→ Reabsorbed back into the presynaptic axon terminal by active transport

9

In the intracellular and extracellular fluids the concentrations are:

→ Extracellular fluid has a high concentration of sodium ions and chlorine ions

→ Intracellular fluid has a high concentration of potassium ions and various negative ions and low concentrations of sodium and chlorine ions

10

The cell membrane is:

Highly permeable to potassium ions
Slightly permeable to sodium ions
Impermeable to large negative ions

→ Therefore there is a tendency for potassium ions to diffuse out of the cell, this makes the cell more negatively charged as its losing positive ions

The potential difference created is called the membrane potential
The resting membrane potential is the membrane potential/difference of unstimulated nerve cells

> -70 mV (millivolts) - This means the potential of the inside of the membrane is 70mV less than that of outside

11

Maintaining the potential difference in two ways

1. Sodium potassium pump
→ Cell activity moves sodium ions out of the cell and potassium ions into the cell using sodium and potassium protein pumps, for every 3 sodium ion molecules released, 2 potassium ion molecules will be brought back

2. Cell membrane is not equally permeable to all ions which means many negatively charged ions are trapped inside the cell

12

Action Potential

When a sufficiently strong stimulus is applied to a nerve fibre, the membrane will become more permeable to sodium ions therefore sodium channels will open and diffuse into cell

→ This enables cell to be more positive inside than the outside and increases the potential difference

If the level of stimulation exceeds 15mV (-70 to -55) it is known as an All or None response and can be passed along axon

→ When it exceeds 15mV it is classified as a sufficiently strong stimulus
→ Doesn’t matter size of impulse, if above 15 it will go if it doesn't nothing will happen
→ ‘passed along axon’ is known as the action potential

The movement of sodium ions is independent to the strength of the stimulus

The flood of sodium ions into the cell causes the inside of the cell to reach a charge of 0 and slightly positive → Depolarisation/switching of charges

To re-polarize the cell, the sodium channels close and potassium ions diffuse out of cell therefore potassium ions open to return and create a negative charge

When potassium channels remain open for longer what is needed the potential drops lower than the resting → hyperpolarized

The rapid depolarisation and repolarisation is called the action potential
The movement of an action potential along a nerve is known as the nerve impulse

13

Nervous system divides into two divisions

Central nervous system

Peripheral nervous system

14

Central nervous sytem

Brain and spinal cord

15

Peripheral nervous system

Nerves, receptors and effectors

16

Peripheral nervous system divides into two divisions

Afferent: carries into to CNS from receptors

Efferent: carries info away from CNS to effectors

17

Afferent division

1. Somatic: carry info from receptors in skin, muscles or joints

2. Visceral: Carry info from receptors in internal organs

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Efferent division

1. Somatic: carry info to skeletal muscles

2. Autonomic: Carry info to involuntary muscles and glands

19

Autonomic divisions

Parasympathetic: rest and digest

Sympathetic: fight or flight

20

What is a receptor

Detects changes in the body's internal or external environment

21

Thermoreceptors purpose

Detect temperatures

22

Thermoreceptors location

Skin - detect external temp

Hypothalamus - detect internal temp

23

Thermoreceptors function

Hypothalamus collects information which can regulated body temperature

24

Osmoreceptors purpose

Detect osmotic pressure

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Osmoreceptors location

Hypothalamus

26

Osmoreceptors function

Stimulate the posterior pituitary to release ADH to regulate osmotic pressure

27

Chemoreceptors purpose

Detects chemicals

28

Chemoreceptors location

Nose and mouth and internally

29

Chemoreceptors function

Receptors detect composition of body fluids (pH, O2 and CO2) and these messages are sent to the respiratory centre to regulate breathing rate

30

Touch receptors purpose

Detect touch

31

Touch receptors location

mostly in the skin

32

Touch receptors function

Detect light touches and harder touches and these messages are sent to the brain to give response

33

Pain receptors prupose

Detect pain

34

Pain receptors location

Skin and mucous membrane

35

Pain receptors function

Stimulated by damage to tissues, excessive heat or chemicals and messages are sent to brain to detect pain

36

Describe the Cerebrum

Many convolutions which increases surface area

Separated by shallow folds called sucli or deep folds called fissures

Deepest fissure - longitudinal fissure which separates brain into right and left hemisphere

37

4 lobes of brain

Frontal
Temporal
Occipital
Parietal

38

Frontal lobe

Important for voluntary movement, expressive language and for managing higher level executive function

39

Occipital Lobe

The occipital lobe is the visual processing area of the brain. It is associated with visuospatial processing, distance and depth perception, colour determination, object and face recognition, and memory formation

40

Temporal lobe

important role in processing affect/emotions, language, and certain aspects of visual perception

41

Parietal lobe

Processes sensory information it receives from the outside world, mainly relating to touch, taste, and temperature

42

Cerebral cortex matter

Grey

43

Tracts

White matter

44

Types of tracts

Connect various areas in the same hemisphere

Carry impulses between hemispheres

Connect to other parts of brain or spinal cord

45

Basal ganglia

Underneath the tracts, grey matter

46

Functional areas of the brain

1. Sensory areas
2. Motor areas
3. Association areas

47

Sensory areas

Interpret impulses from receptors, perception of sense

48

Motor areas

Control muscular movements, initiation and control of voluntary muscle

49

Association areas

Intellectual and emotional processes, involved in activities such as thinking, reasoning, learning, memory

50

Corpus Callosum

Wide band of nerve fibres underneath the cerebrum

Enables both hemispheres to communicated

51

Cerebellum Location

Back of the cerebrum

52

Role of Cerebellum

Receives constant input from the senses

Maintains muscles tone and posture

53

Hypothalamus location

Located in middle of brain

54

Hypothalamus function

Controls homeostasis
Body temperatures
Autonomic nervous system

55

Medulla Olbongata

1. Cardiac centre - regulated rate and force of heartbeat

2. Respiratory centre - control of rate and depth of breathing

3. Vasomotor centre - regulated diameter of blood vessels

56

Protection of CNS - Bone

Hardness of the cranium encases the brain

57

Protection of CNS - Meninges

1. Dura mater - tough fibrous, prevents brain from moving around

2. Arachnoid mater - loose mesh fibres

3. Pia mater - creates a seal that protect brain from infection

58

Cerebrospinal fluid properties

Clear watery fluid, contains glucose, protein, urea and salta

59

Functions of cerebrospinal fluid

Protection - shock absorber

Support - brain is suspended in cranium

Transport - takes nutrients to cells and wastes away

60

Reflex

Triggered by a stimulus
Involuntary
Rapid
Stereotypes

61

Reflex arc

1. Receptor in the end of a sensory neuron detect a change in the environment and reacts to this stimulus by producing a nerve impulse

2. Sensory neuron carries impulse to spinal cord

3. Information is processed in CNS, nerve impulse is passed across a synapse to a motor neuron via an interneuron

4. Motor neuron then carries nerve impulse to an effector

5. The effector receives nerve impulse and carries out an appropriate response

62

Protective reflexes

Blinking
Sneezing
Coughing

63

Exocrine Glands

Secrete into a duct that carries the secretion to the body surface

64

Endocrine glands

Secrete hormones into the extracellular fluid that surrounds the cells making up the gland

65

Pituitary gland

Lies just underneath the hypothalamus and is joined by the stalk called the infundibulum

Has two lobes

66

Anterior lobe

Connected to the hypothalamus via blood vessels

Produces own hormones

Releases hormones via chemical stimulation

67

Posterior lobe

Connected to hypothalamus by nerve fibres

Releases hormones from hypothalamus

Releases hormones via nervous stimulation

68

Transmission of hormones from the posterior lobe

1. Hormones transport down the axons of the nerve cells to the posterior lobe

2. There are stored in the posterior lobe until required

3. Their release is triggered by a nervous impulse which is initiated by the hypothalamus and conducted along the nerve cell extensions

69

Hormones

Change functioning of cells by changing the type, activities or quantities of proteins produced

70

Hormones Functions

Activate certain genes so that a particular enzyme or protein produced

Change the shape or structure of an enzyme

Change the rate of production of an enzyme or protein

71

Protein and Amine hormones

1. Attach to receptors on surface of cell membrane of target cell

2. This combination of hormone and receptor causes a secondary messenger to diffuse through the cell and activate particular enzymes within the cytoplasm

3. Faster acting hormones

72

Steroid hormones

1. Enter target cells and combine with receptor protein inside the cytoplasm of cell

2. Lipid soluble so easily diffuse through cell membrane

3. The hormone-receptor complex then enters the nucleus and activates genes controlling formation of particular proteins

4. Slower acting hormones

73

Anterior lobe Hormones

1. Follicle Stimulating Hormone: Ovaries and testes : growth of follicles, production of sperm

2. Luteinising hormone: ovaries and testes: ovulation and maintenance or corpus luteum and secretion of testosterone

3. Growth hormone: all cells: growth and protein synthesis

4. Thyroid-stimulating hormone: thyroid gland: secretion of hormones from the thyroid

5. Adrenocorticotropic hormone: adrenal cortex: secretion of hormones from the adrenal cortex

6. Prolactin: mammary glands: milk production

74

Posterior lobe

Antidiuretic hormone
1. Kidneys: reabsorption
2. Uterus: contractions of uterus during childbirth

Oxytocin
1. Mammary glands: release of milk

75

Thyroid

Thryoxine: Most body cells, increases metabolic rate, oxygen consumption and heat production

Calcitonin: bones, kidneys, decreases calcium and phosphate in the blood

76

Parathyroid

Parathyroid: bones and kidneys, increases level of calcium in blood

77

Thymus

Thymosis: T-lymphocytes, stimulates development and maturation of t-lymphotcytes

78

Adrenal cortex

1. Corticosteroids: kidneys, increases reabsorption of sodium ions and excretion of potassium ions

2. Cortisol: most body cells, promotes normal metabolism, helps body deal with stress, promotes damages tissues

79

Adrenal medulla

Adrenaline: most body tissues, prepares the body for fight or flight response

80

Pancreas

Insulin: most body cells, stimulates uptake of glucose, lowers blood glucose level

Glucagon: liver, stimulates breakdown of glycogen and fat

81

Testes

Androgens: many tissues, stimulate sperm production, growth of skeleton, development of male sexual characteristics

82

Ovaries

Oestrogen: many tissues, stimulate development of female sexual characteristics

Progesterone: uterus and mammary glands, regulates menstural cycle and pregnancy

83

Homeostasis

Maintenance of internal environment

84

Feedback system

The response causes the stimulus a direction opposite to that of the original stimulus

85

What does a feedback system consists of

1. Stimulus
2. Receptor
3. Modulator
4. Effector
5. Feedback

86

Positive feedback

The response to stimulus reinforcer and intensifies the stimulus

87

Heat Gain Internal

Heat is a by-product of cellular respiration

Metabolic rate, which energy is released by the breakdown of food

Metabolic rate is affected by exercise, stress and body temperature

88

Heat Gain External

Radiation or conduction from surroundings

89

Heat Loss Internal

Evaporation of water from skin and lungs

Warm air breathed out

Warm urine and faeces

90

heat Loss External

Radiation

Conduction

Convection to surroundings

91

Conduction

Transfer of heat via direct contact with another object

Involves the exchange of heat from molecule of higher temperature to molecule of lower temperature when they vibrate and touch

92

Convection

Transfer to heat to air around the body

When cool air makes contact with our body it heats up and becomes less dense, less dense air rises and is replaced by cooler more dense air

93

Radiation

Transfer to heat without contact

All objects emit heat to their surroundings by radiation

Heat will radiate to cooler objects around you like the floor and walls

94

Evaporation

Transfer of heat through evaporation of liquid to gas

Heat energy is required to change from a lower energy liquid phase to a higher energy gas phase

This heat energy is absorbed from the surface of the skin, which then cools when the water evaporates, meaning heat is lost

95

Temperature tolerance

1. Heat stroke, body temp rises by regulatory mechanisms are not working

2. Heat exhaustion, result of extreme sweating and vasodilation

3. Hypothermia, if cored body temp balls below 33 degrees

96

Temperature receptors

1. Peripheral thermorecepotors skin and mucous membranes