Brain and Nervous System

Intermediate 2 Biology

The Brain

The brain

• The brain is at the top of the spinal cord and is protected by the skull.

Learning Objectives

• Identify the main structures of the brain

(cerebrum, cerebellum, medulla and

hypothalamus) and state their

functions

Structure of the Brain

• There are four main areas in the brain: – the cerebrum which controls memory,

personality and conscious thought

– the cerebellum which controls balance and co-ordination of movement

– the medulla which controls heart rate and breathing rate

– the hypothalamus which is the regulating centre for temperature and water balance

Structure of the Brain

cerebrum

cerebellum

Medulla

Oblongata Pituitary gland Spinal cord

hypothalamus

The

Cerebral

Cortex

The Brain

Sensory Area Motor Area

Cerebrum

• The cerebrum is split into left and right

cerebral hemispheres.

• Each region is discrete an performs it’s

own function

• The left cerebral hemisphere has

sensory and motor strips in the centre.

Sensory Area

• Each sensory area receives information

from sense organs (receptors)

• Information is passed onto other areas of

the brain to be analysed

• The size of the sensory area allocated to

each region of the body is in proportion

to the relative number of receptor cells

– The more sensitive the body part, the larger

the region of the sensory strip

The sensory homunculus

Body parts

are drawn in

proportion to

their sensitivity

Motor Area

• Each motor area consists of motor

neurones which send out impulses to

bring about voluntary movements of

skeletal muscles

• The size of each motor area is in

proportion to mobility resulting from the

relative number of motor endings present

– the more mobile the part, the larger the

region of the motor area

The motor homunculus

Body parts

are drawn in

proportion to

their mobility

and fine

motor control

Learning Objectives

• Describe the function of the nervous

system

• State the components of the central

nervous system

• Describe a reflex arc and explain its

purpose

• What does your nervous

system do for you?

The Nervous System

The Nervous System

• The nervous system controls our bodies and helps us respond to external stimuli.

• There are two main parts: – Central nervous system – brain and spinal

cord

– Peripheral nervous system – the rest of the nervous system.

• The nervous system works by sending electrical impulses along neurones (nerve cells).

Responding to external Stimuli

• Sense Organs contain receptor cells

detect changes in the environment

• These changes are called Stimuli

• Make a list of receptor cells in the

human body, and write down what

they are sensitive to.

Sensitivity

• Receptor cells can be found in – Eyes

• sensitive to light

– Ears • sensitive to sound

• respond to changes in position and enable us to keep our balance.

– Tongue and nose • sensitive to chemicals, enable us to taste and smell.

– Skin • sensitive to touch, pressure, pain and temperature

The Nervous System

• The information from the sense organs to the central nervous system along neurones

• There are two main parts to the nervous system: – Central nervous system

• brain and spinal cord

– Peripheral Nervous System • A network of neurones

Responding to changes

Receptors

in the

body

detect a

change

inside or

outside of

the body

Central

nervous

system

co-ordinates

the body’s

responses

effectors

cause a

response

by moving

part of the

body or

secreting a

hormone

Reflex Arc

Reflex Action a rapid, automatic, involuntary response to a stimulus

Reflex Action

(extension notes)

• Some responses to stimuli are

automatic and rapid these are called

reflex actions.

• In a reflex action three types of

neurone are involved sensory, relay

and motor neurones.

• In a reflex action:

– Impulses from a receptor pass along a sensory neurone to the central nervous system.

– At a junction (synapse) between a sensory neurone and a relay neurone in the CNS, a chemical is released which causes an impulse to be sent along a relay neurone.

– A chemical is then released at the synapse

between a relay neurone and a motor

neurone in the CNS. This causes impulses to

be sent along a motor neurone to the organ

(effector), which brings about the response.

– Effector is either a muscle or a gland. A

muscle responds by contracting, a gland by

releasing chemical substances.