Biopsychology Revision
The Nervous System:
Central nervous system (CNS):
- Consists of the brain and spinal cord
- Where all processing of info is done/decisions made
Brain:
- Divided into 2 hemispheres
- Chief executive of the body
- The control centre for: walking, talking, swallowing,
breathing, taste, smell, heart rate and digestion
- Controls all thinking functions, emotions, behaviour and
all intellectual (cognitive) activities, such as how we attend to things, how we perceive
and understand the world and its physical surroundings, how we learn etc.
The Spinal cord:
- Extension of the brain
- Is the main pathway for transporting messages to and from the brain to the peripheral
nervous system
- Spinal cord is protected by the spinal column (bones called vertebrae)
Peripheral nervous system:
- Brings info from the senses back to the CNS and transmits info from the CNS to the
muscles and glands
- Relays info (in the form of nerve impulses) from the CNS to the rest of the body, and
from the body back to the CNS (e.g. CNS detected danger, message sent to leg
muscles to run or sensory receptors in skin detect heat, message sent to CNS to
withdraw hand)
Somatic nervous system:
- Receives info from the senses and transmits it to the CNS
- Transmits info from the CNS to direct movement of the muscles
- Somatic = relating to the body
Autonomic nervous system:
- Responsible for all vital functions (e.g. heartbeat, breathing,
digestion)
- Transmits info from and to the internal body organs (e.g. liver and
lungs)
- Operates automatically or involuntarily
Sympathetic nervous system:
- Stimulates cation (heart rate and blood pressure)
- Involved in “fight or flight” response by preparing for action
Parasympathetic nervous system:
- Slows functions (heart rate and blood pressure)
, - Involved in the “fight or flight” response by returning the body to normal resting state
Structure of Nerves:
Neurons (also called neurons or nerve cells) are the fundamental units of the brain and
nervous system, the cells responsible for receiving sensory input from the external world, for
sending motor commands to our muscles, and for transforming and relaying the electrical
signals at every step in between.
Neuron structure:
The cell body contains the nucleus (chromosomes), from the
cell body. The dendrites extend from the cell body. They carry
electrical impulses from other neurons towards the cell body.
The axon is an extension of the neuron, it carries the impulses
away from the cell body. It is covered by a sheath of myelin, a
fatty substance. The main purpose of the myelin sheath is to
increase the speed at which impulses propagate. There are
breaks of between 0.2 and 2 mm in the myelin sheath, these
are called nodes of Ranvier. Action potentials (nerve
impulses) travelling down the axon "jump" from node to node.
This speeds up the transmission.
Neurons: the nerve cells, the human brain has about 100 billion neurons. There are 3
types:
Sensory Neuron:
- Carry nerve impulses from sensory receptors (e.g. receptors for vision, taste, touch)
to the spinal cord and the brain.
- They convert information from these sensory receptors into neural impulses. When
the impulses reach the brain, they are translated into sensations (e.g. visual input,
heat, pain etc.) so that the organism can react appropriately.
- Not all sensory information travels to the brain, with some neurons terminating in the
spinal cord. This allows reflex actions to concur quickly without the delay of sending
the impulses to the brain.
Relay Neuron:
- Most neurons are relay neurons. They lie between the sensory input and the motor
output. Relay neurons allow sensory and motor neurons to communicate with each
other. They lie wholly within the brain and spinal cord.
Motor Neuron
- Refers to neurons which conduct signals from the CNS to effector organs such as
muscles. Their cell bodies are in the CNS but they have long axons which form
part of the PNS. Motor neurons form synapses with muscles and control their
contractions. When stimulated, the motor neuron releases neurotransmitters that
bind to receptors on the muscles and triggers a response which leads to muscle
, movement. When the axon of a motor neuron fires, the muscle with it which has
formed synapses contracts. The strength of the muscle contraction depends on the
rate of firing of the axons of motor neurons that control it. Muscle relaxation is caused
by inhibition of the motor neuron.
The Reflex Arc:
The nervous impulse is transmitted as follows:
Synaptic Transmission:
Synaptic Transmission: A synapse is the gap between two
neurons. Chemicals travel across this gap and stimulate the
next neuron. The gap between the synapse is 20000 times
the width of a piece of paper.
Once an electrical impulse (action potential) has arrived at
the terminal button at the end of the axon, it needs to be
transferred to another neuron or to a tissue. In order to do
this it must cross the gap (aka the synapse) between the
presynaptic neuron and the postsynaptic neuron. At the end
of the axon of the nerve cells are a number of sacs known
as synaptic vesicles which contain the chneitcal messengers
that assist in the transfer of the impulse, neurotransmitters.
As the action potential reaches the synaptic vesticles, it
causes them to release their contents.
Neurotransmitters diffuse across the gap:
The neurotransmitters diffuse across the gap between the pre and post synaptic cell, where
it binds to specialised receptor cells.
Some neurotransmitters are excitatory and some are inhibitory. Excitatory neurotransmitters
(e.g. noradrenaline) make the postsynaptic cell more likely to fire, whereas inhibitory
neurotransmitters (e.g. GABA) make them less likely to fire. For example, if an excitatory
neurotransmitter like noradrenaline binds to the postsynaptic receptors it will cause an
electrical charge in the cell membrane which results in an excitatory postsynaptic potential
(EPSP), which makes the postsynaptic cell more likely to fire. Conversely, if an inhibitory
neurotransmitter like GABA binds to the postsynaptic receptors it will result in an inhibitory
postsynaptic potential (IPSP), which makes the postsynaptic cell less likely to fire.
A nerve cell can received both excitatory and inhibitory neurotransmitters at the same time
but the likelihood of the cell firing is determined by adding up the EPSPs and the IPSPs. The
