Download File - Ms Curran`s Leaving Certificate Biology

The Nervous System
Nervous system is divided into 2 parts:
1.
Central Nervous System (CNS)
 Brain and Spinal Cord
2.
Peripheral Nervous System (PNS)
 Nerves that carry messages between CNS & rest
of body.
To make the correct response to a stimulus,
4 processes are involved
1.
2.
3.
4.
Reception, a stimulus is detected, this is the
function of neurons & sense organs
Transmission, msg passes along neurons
Receptors -> PNS -> CNS
CNS -> PNS -> Effectors (muscles)
Integration, Msgs are sorted and processed
and a response decided upon.
Response, carried out by effectors when
stimulated by neurons
Neurons

Is a nerve cell, specialised to carry info
3 types of neurons
Sensory
To Brain
Motor
Interneuron's
Between Sensory
& Motor
To muscles
Structure of
Neurons
Neurons vary in size,
neurons in the brain
are tiny, neurons
connecting the spine
& feet may be over 1
metre long.
Structure of Neurons
Cell Body-contains nucleus & organelles &
produce neurotransmitter chemicals.
Group of cell bodies outside CNS called Ganglion


Dendrites-carry impulses towards the centre of
the neuron to the cell body

Axon- carry impulses away from the centre of
the neuron to the cell body
Structure of Neurons

Neurotransmitter vesicles-at the end of axons,
these swellings release chemicals that carry
the impulse from 1 cell to another. Chemicals
called neurotransmitters

Schwann cells, located along neurons, make
myelin sheath.

Myelin sheath, fat rich membrane that
insulates the electrical impulses (MS patients
lack this)
Interneurons
 Short neurons found
in CNS.
 Not enclosed in
Myelin sheath
 They connect motor
& sensory nerves
Movement of Impulses
When a neuron receives a stimulus an
electrical impulse travels along the dendrite &
axon to the neurotransmitter swellings
 The movement of the electrical impulse along
a neuron involves the movement of ions.
 When an neuron is Not carrying an impulse
ions are pumped in & out of the axon. This
results in the inside of the axon being –ive and
the outside +ive
 Threshold, is the minimum stimulus needed to
cause an impulse

Movement of Impulses
Once the threshold is reached the axon
changes its permeability to ions
 At the site of stimulation the inside of the axon
becomes +ive & the outside –ive.
 This change in charge causes the next section
of the axon to alter its permeability
 A chain reaction is set up & a movement of
+ive charges runs along the inside of the Axon.
 Energy (ATP) is needed to cause these changes
 Diagram 34.6 pg 322

Synapses
Neurons are not connected to each other, they
are separated by a small gap, Synaptic cleft.
 Synapse is the region where 2 neurons come
into close contact.
 Electrical impulses cannot cross a synapse,
instead they stimulate the neurotransmitter
swellings to release a chemical substance
(neurotransmitters), which diffuse across the
synaptic cleft

Synapse
After the nerotransmitters diffuse across the
synaptic cleft the combine with receptors on
the postsynaptic neuron.
 This causes an impulse to be regenerated
 The neurotransmitter is then broken down
by enzymes. The digested NTs are
reabsorbed into the neurotransmitter
swellings and recycled.

The CNS-The Brain
The brain contains over 1200 million neurons
 The brain & spinal cord is protected by bone &
3 membranes called Meninges
 Meningitis is an inflammation of these
Meninges caused by virus or bacteria
 Viral meningitis is less severe
 Bacterial meningitis can lead to death

Structure of the Brain
Cerebrum
Largest part
of the brain
Right controls
left Left controls
right Strokes
Outer part called
cerebral cortex
controls
voluntary
movements
Structure of the Brain
Cerebellum
2nd
largest
controls
muscular
coordination
involuntary
once the
process has
been learned
Medula Oblongata
Controls breathing,
blood pressure,
swallowing,
coughing
Connects the
spinal cord with
the rest of the
brain
Structure of the Brain
Hypothalamus
located below
the thalamus
regulates the
internal
environment
Thalamus
located below
the cerebrum
sorting
centre
links with
pituitary
gland
Spinal Cord
Composed of nerve tissue, surrounded by
vertebrae which protects it.
 Transmits impulses to & from the brain
 Is located in the neural canal of the vertebrate
 The neural canal is lined by the meninges &
contains cerebrospinal fluid
 Dorsal root carries sensory neurons into the
spinal cord & the ventral root carries motor
neurons out
 Dorsal & ventral roots combine to form 31 pairs
of spinal nerves

Reflex Action

Is a quick, automatic response to a particular
stimulus.