The nervous system Flashcards
(29 cards)
What is the nervous system?
A specialised network of cells in the human body and is our primary internal communication system.
What are the nervous system’s 2 main functions?
- to collect, process and respond to information in the environment.
- to co-ordinate the working of different organs and cells
The major subdivisions of the human nervous system
Human Nervous System -> CNS and PNS
Central Nervous System (CNS) -> Brain and Spinal Cord
Peripheral Nervous System (PNS) -> Autonomic and Somatic
Nervous Systems
Autonomic Nervous System -> Sympathetic and
Parasympathetic Nervous
Systems
What are the functions of the CNS?
It passes messages to and from the brain and connects nerves to the PNS.
What is the role of the spinal cord in the CNS?
It relays information between the brain and the rest of the body, allowing the brain to regulate bodily processes. It is also responsible for some simple reflex actions.
What is the role of the spinal cord in the CNS?
It relays information between the brain and the rest of the body, allowing the brain to regulate bodily processes. It is also responsible for some simple reflex actions.
What is the role of the brain in the CNS?
It is the centre of all conscious awareness. It’s outer layer, the cerebral cortex, is highly developed in humans. It can be divided into 4 main areas.
Describe the cerebrum.
It is the largest part of the brain and is further divided into 4 lobes (frontal, temporal, occipital and parietal). Each lobe has a different primary function. It is also divided into hemispheres, each of which having a different primary function. The hemispheres communicate via the corpus collosum.
Describe the cerebellum.
It controls a person’s motor skills and balance and is located at the back of the brain under the cerebrum. Problems in this area cause issues with speech and motor production and epilepsy.
Describe the Diencephalon.
It contains the thalamus and the hypothalamus and is found in the centre of the brain.
The thalamus is a relay station - it receives information from the senses and sends the information to the correct area of the brain to be processed.
The hypothalamus controls homeostasis and links the nervous system with the endocrine system.
Describe the brain stem.
It regulates the automatic functions that are essential for life and is found at the base of the brain. Impulses pass between the brain and spinal cord via the brain stem.
Describe the PNS.
The PNS is all the nerves outside the brain and spinal cord. It transmits messages via millions of neurons between the body and the CNS. It is subdivided into the somatic and autonomic nervous systems.
Describe the somatic nervous system.
This is the part of the PNS that is responsible for carrying sensory and motor information to and from the CNS. It carries sensory information from the environment to the brain and provides muscle responses via the motor pathways.
Describe the autonomic nervous system.
It carries out actions without your conscious awareness, governing vital bodily functions such as breathing, heart rate and digestion.
The autonomic nervous system is subdivided into the sympathetic and parasympathetic nervous systems. Their actions are mostly antagonistic.
Describe the sympathetic nervous system.
It activates the fight-or-flight response and prepares the body to expend energy. It generally uses the neurotransmitter adrenaline, which has an excitatory effect.
Describe the parasympathetic nervous system.
It co-ordinates recovery once the threat has passed. It also maintains and conserves body energy and functions. It generally uses the neurotransmitter acetylcholine, which has an inhibitory effect.
What are neurons?
Neurons are the cells which make up the nervous system. They transmit pulses of electrical activity called ‘action potential’.
Describe a neuron.
Neurons vary in size from less than a millimetre up to a metre in length, but all share the same basic structure:
-The cell body (soma) contains the cell nucleus which holds
the genetic material of the cell
-The dendrites are branch-like structures protruding from the
soma which carry impulses from neighbouring neurons
towards the soma
-The axon carries the impulses away from the soma down the
length of the neuron
-The myelin sheath is the fatty layer which surrounds the
axon in order to protect it and speed up transmission
-The nodes of Ranvier are small gaps in the myelin sheath
that speed up transmission by forcing the impulse to jump
across the gaps
-The terminal buttons communicate with the next neuron
across the synaptic cleft
Describe sensory neurons.
They carry nerve impulses from sensory receptors and tell the brain about the external and internal environment by processing information from the senses.
They carry messages from the PNS to the CNS.
Some sensory information stops at the spinal cord allowing a reflex to happen.
They have long dendrites and short axons.
Describe relay neurons.
They carry messages from one part of the CNS to another and allow sensory and motor neurons to communicate.
They lie wholly within the spinal cord.
They have short dendrites and short axons.
Describe motor neurons.
They carry signals from the CNS which help organs, glands and muscles (effectors) function.
When stimulated they release neurotransmitters that bind to receptors on the muscle and trigger response, leading to movement.
They form synapses with muscles and control their contractions.
Muscle relaxation is caused by inhibition of the neuron.
They have short dendrites and long axons.
Why can information only travel in one direction at a synapse?
Neurotransmitters only bind to specific receptor sites on the postsynaptic neuron. This is an example of the lock and key model. The dendrites of the postsynaptic neuron do not contain synaptic vesicles, and so cannot release neurotransmitters in the opposite direction. Similarly, receptor cells are not present on the axon of the presynaptic neuron, and so information cannot travel in both directions.
How do cells pass messages on between neurons?
- Synaptic transmission
- Chemically
How do cells pass messages on within neurons?
- Action potential
- Electrically
