The Human Nervous System

Not all topics

What is homeostasis?

The regulation of the internal conditions of a cell/organism to maintain optimum conditions for functions in response to internal/external changes

What does homeostasis maintain?

Optimal conditions for enzyme function and all cell functions

What does homeostasis control?

• Blood glucose concentration

• Body temperature

• Water levels

What kind of responses may automatic control systems involve?

Nervous responses or chemical responses

What do all control centres include?

• Receptors

• Coordination centres

• Effectors

What are receptors?

Cells that detect stimuli

What are stimuli?

Changes in the environment

What do coordination centres do?

Receive and process information from receptors (brain, spinal cord, pancreas)

What are effectors?

Muscles or gland which bring about responses which restore optimum levels

Name 5 ways nerve cells have adapted

• Lots of dendrites

• Axon

• Synapses

• Lots of mitochondria in synapses

• Myelin sheath

What are nerve cells specialised to do?

To provide a rapid communication system, carrying electrical impulses around the body

What do lots of dendrites do in a nerve cell?

Make connections to other nerve cells

What does the axon do in a nerve cell?

Carries nerve impulses from one place to another

What do the synapses do in a nerve cell?

Pass impulses to another nerve cell or between a nerve cell + muscle using special transmitter chemicals

Why do the synapses need lots of mitochondria?

To provide energy needed to make transmitter chemicals

What does the myelin sheath do in the nerve cell?

Provide insulation

What does the nervous system enable humans to do?

React to their surrounding and coordinate their behaviour

Describe the order of the nervous system in shorthand

Stimulus → Receptor → Coordinator → Effector → Response

Describe the order of the nervous system in detail

• Information from receptors passes along sensory neurones as electrical impulses to the central nervous system

• The CNS coordinates the response and sends impulses along motor neurones which are muscles contracting or glands secreting hormones

Describe the order of the reflex arc

• Receptor stimulated by stimulus and passes an electrical impulse along a sensory neurone to the CNS

• The impulse arrives at a synapse and a chemical is released

• The chemical diffuses across the synapse to the relay neurone

• A chemical diffuses across the synapse between the relay and motor neurone

• The effector organ is stimulated to respond

What is a synapse?

Junctions which form physical gaps between neurones

How do the impulses cross the synapse?

By diffusing a chemical across the gap

Reflex actions are ? and ?

Automatic and rapid

Give 2 reasons why we need reflex actions

• To help avoid danger

• To take care of basic body functions e.g. breathing and moving food through digestive system

What is the brain made of?

Billions of interconnected neurones and has different regions to carry out different functions

Function of the cerebral cortex

Concerned with consciousness, intelligence, memory and language

Function of the cerebellum

Concerned mainly with coordinating muscular activity and balance

Function of the medulla

Concerned with unconscious activities e.g. controlling heartbeat, gut movements and breathing

Give reasons why it is difficult to investigate the brain

• The brain is inside the skull

• The brain is complex

• The brain is delicate

• Some regions can’t be studied in isolation

• Accidental damage could lead to speech/motor issues and personality change

• Ethical considerations - those with severe issues can’t consent

• Nervous tissue does not repair as easily as others - irreversible damage

How have scientists been able to give functions to parts of the brain?

• Studying patients with brain damage

• Electrically stimulating different parts of the brain

• Using MRI scanning techniques

What is the eye?

A sense organ containing receptors sensitive to light intensity and colour

Function of retina

Contains light receptors which sends impulses to the brain along sensory neurones in the optic nerve to interpret a visual image

Function of optic nerve

Carries impulses from the eye to the brain

What is the sclera?

Tough white outer layer of the eye to protect from injury

Function of cornea

Refracts light as it enters eye to focus on retina

Function of iris

Controls size of pupil to control amount of light reaching retina to reduce damage

Function of ciliary muscles and suspensory ligaments

Fine tunes the focusing of the light rays

What is accommodation?

The process of changing the shape of the lens to focus on near or distant objects

How does the eye focus on a near object?

• Ciliary muscles contract

• Suspensory ligaments loosen

• Lens is thicker and refracts light rays strongly

How does the eye focus on a distant object?

• Ciliary muscles relax

• Suspensory ligaments pulled tight

• Lens is pulled thin and slightly refracts rays

What is myopia?

Short sightedness

What is hyperopia?

Long sightedness

What causes myopia?

• Lens is too thick and curved

• Eyeball is too elongated

• Light rays in front of retina

What causes hyperopia?

• Lens less elastic

• Eyeball too short

• Light rays behind the retina

What type of lens fixes myopia?

Concave lens

What type of lens fixes hyperopia?

Convex lens

Name 5 accommodation techniques

• Spectacle lenses

• Hard contact lenses

• Soft contact lenses

• Laser surgery = changes shape of eye

• Replacement lens

What is body temperature controlled by?

The thermoregulatory centre in the brain

What does the thermoregulatory centre contain?

Receptors sensitive to the temperature of the blood

What does the skin contain?

Temperature receptors that send nervous impulses to the thermoregulatory centre

What happens if body temperature is too high?

• Blood vessels dilate (vasodilation)

• Sweat produced from sweat glands

• These mechanisms cause an energy transfer from skin to environment

What happens if body temperature is too low?

• Blood vessels constrict (vasoconstriction)

• Sweating stops

• Skeletal muscles contract (shiver)

How does vasodilation change temp?

Increases blood flow = skin flushes = transfer more energy by radiation to surroundings

How does sweat change temp?

Water evaporates from skin = transfers energy to environment

How does skeletal muscles contracting change temp?

Contractions need respiration (exothermic process) = energy transferred from exothermic reaction raises body temperature

What is normal body temperature

37 degrees celsius