Lessons 01 - 05 Flashcards
(36 cards)
The Nervous System
A specialised network of cells in the human body and is our PRIMARY INTERNAL COMMUNICATION SYSTEM.
Functions:
- To collect, process and respond to information in the environment
- To coordinate the working of different organs and cells in the body
Divided into the CNS and PNS
The Central Nervous System
Made up of the spinal cord and brain
The brain is the CENTRE OF ALL CONSCIOUS AWARENESS. The outer layer, the cerebral cortex, is highly developed in humans and is what distinguishes our higher mental functions from those of animals. Only a few living creatures (jellyfish, sponges, sea squirts) do not have a brain. It is divided into the left hemisphere and the right hemisphere
The spinal cord is an extension of the brain, which is responsible for REFLEX ACTIONS (e.g. pulling your hand away from a fire). It passes messages to and from the brain and connects nerves to the PNS
The Peripheral Nervous System
It TRANSMITS MESSAGES via millions of neurons (nerve cells) to and from the CNS. It is divided into the Autonomic Nervous System (ANS) and the Somatic Nervous System (SNS)
ANS: governs VITAL FUNCTIONS in the body such as breathing, heart rate, digestion, sexual arousal and stress responses
SNS: controls MUSCLE MOVEMENT and receives information from sensory receptors
The Spinal Cord
The main function is to RELAY INFORMATION between the brain and the rest of the body, allowing the brain to monitor and regulate bodily processes (digestion, breathing) and to coordinate voluntary movements.
The spinal cord is connected to different parts of the body by pairs of spinal NERVES, which connect the specific muscles and glands.
The spinal cord also contains circuits of nerve cells that enable us to perform simple REFLEXES without the direct involvement of the brain (e.g. pulling your hand away from something hot)
The Brain
The centre of all conscious awareness
Four main divisions:
- The cerebrum
- The cerebellum
- The diencephalon
- The brain stem
The Cerebrum
The largest part of the brain. It is split into four different lobes, each has a different primary function: the frontal lobe, temporal lobe, parietal lobe and occipital lobe. It also split into two halves called cerebral hemispheres. Each hemisphere is specialised for particular behaviours and the two hemispheres communicate via the corpus callosum
The Cerebellum
It sits at the back of the cerebrum and is involved in controlling a person’s MOTOR SKILLS AND BALANCE, coordinating the muscles to allow precise movements
The Diencephalon
It lies beneath the cerebrum and on top of the brain stem. It contains the thalamus and hypothalamus
The Brain Stem
This is responsible for REGULATING AUTOMATIC FUNCTIONS essential for living (breathing, heartbeat and swallowing). Also motor and sensory neurons travel through the brain stem, allowing IMPULSES to pass between the brain and the spinal cord
Diagram of the brain
DO I KNOW IT????????
The PNS in detail: the Somatic Nervous System
It controls VOLUNTARY MOVEMENT and is under conscious control
Made up of 12 pairs of cranial nerves (nerves that emerge directly from the underside of the brain) and 31 pairs of spinal nerves (nerves from the spinal cord)
The nerves have both sensory and motor neurons.
It is also involved in REFLEX actions without the involvement of the CNS and allows the reflex to occur very quickly
The control centre is in the motor cortex part of the brain
The role is to to CARRY SENSORY INFORMATION from the outside world to the brain and provide MUSCLE RESPONSES via the motor pathway
The PNS in detail: the Autonomic Nervous System
It regulates INVOLUNTARY ACTIONS (heart beats, digesting food etc.), so is responsible for regulating automatic internal bodily responses
The control centre is in the brain stem
It plays an important role in HOMEOSTASIS
It consists of only motor pathways
Both the sympathetic and parasympathetic nervous systems regulate the same organs
The PNS in detail: the Sympathetic Nervous System (a component of the ANS)
Is involved in responses that help us deal with emergencies (FIGHT/FLIGHT), such as increasing heart rate and blood pressure and dilating blood vessels
Neurons travel to almost every organ and gland within the body, preparing it for RAPID ACTION (e.g. the sympathetic nervous system causes the body to release stored energy, pupils to dilate, hair to stand on end etc.)
The PNS in detail: the Parasympathetic Nervous System (a component of the ANS)
This RELAXES a person AFTER the emergency has passed and returns us to our ‘normal’ resting state (e.g. it slows the heartbeat down and reduces blood pressure. It also starts digestion again)
Sensory neurons
These CARRY messages from the PNS to the CNS. They have LONG dendrites and SHORT axons
They are found in RECEPTORS (e.g. eyes, ears, tongue, skin) and carry nerve impulses to the spinal cord and brain. When the impulses reach the brain, they are translated into ‘sensations’ (e.g. vision, hearing, taste and touch). Not all sensory neurons reach the brain, as some stop at the spinal cord allowing for quick reflex actions
Relay neurons
These CONNECT the sensory neurons to the motor or other relay neurons. They have SHORT dendrites and SHORT axons
They are found in the brain and spinal cord and allow sensory and motor neurons to communicate
Motor neurons
These CONNECT the CNS to effectors such as muscles and glands. They have SHORT dendrites and LONG axons
They control MUSCLE MOVEMENTS. When motor neurons are stimulated, they release neurotransmitters that bind to the receptors or muscles to trigger a response, which leads to movement
Structure of a neuron
[image in booklet]
Neurons vary in size from less than a millimetre to over a metre
The cell body (or soma) include NUCLEUS, which contains the genetic material of the cell. Dendrites (branch-like structures) stick out of the cell body and carry nerve impulses from neighbouring neurons TOWARDS the cell body
The axon carries the impulses AWAY from the cell body down the length of the neuron. The axon is covered in a fatty layer of myelin sheath (relay neurons do not have a myelin sheath), that PROTECTS the axon and speeds up electrical transmission of the impulse
The myelin sheath is segmented by gaps called nodes of Ranvier. These SPEED UP the transmission of the impulse by forcing it to ‘jump’ across the gaps along the axon.
At the end of the axon are terminal buttons (axon terminals) that COMMUNICATE with the next neuron in the chain across the synapse, ready for synaptic transmission
Synaptic Transmission
Refers to the process by which a nerve impulse passes across the synaptic cleft from one neuron (the presynaptic neuron) to another (the postsynaptic neuron)
When in resting state, the inside of the cell is negatively charged. When activated by a stimulus, the inside of the cell becomes positively charged for a split second, causing an ACTION POTENTIAL to occur. This creates an electrical IMPULSE that travels down the axon towards the end of the neuron (this process is electric transmission).
Once an action potential has arrived at the axon terminal, it needs to cross the synaptic cleft (the physical gap between the neurons). On the axon terminal, there are synaptic VESICLES (sacs) that contain neurotransmitters that help in the transfer of the action potential.
EXOCYTOSIS happens
The released neurotransmitter DIFFUSES across the synaptic gap where it binds to specialised receptors, which are activated.
RE-UPTAKE happens
Synapse
It includes the end of the pre-synaptic neuron, the membrane of the post-synaptic neuron and the gap in between (the synaptic cleft)
Exocytosis
When the action potential reaches the vesicles, it causes them to RELEASE their contents (neurotransmitters)
Re-uptake
This terminates the effects of synaptic transmission
The neurotransmitter is TAKEN UP again by the pre-synaptic neuron where it is stored for later release. The QUICKER the neurotransmitter is taken back, the SHORTER the effects
Neurotransmitters
CHEMICAL MESSENGERS that carry signals from the pre-synaptic neuron across the synaptic gap to the receptor site on the post-synaptic neuron.
They can be classed as either excitatory or inhibitory in their action
A nerve cell can receive both EPSPs and IPSPs at the same time. The likelihood of the cell firing is determined by adding up the excitatory and inhibitory synaptic input. The net result (summation) determines whether the cell fires or not.
Inhibitory neurotransmitters
They are generally responsible for CALMING the mind and body, including sleep and filtering out unnecessary excitatory signals
An inhibitory neurotransmitter binding to a post-synaptic receptor results in an inhibitory post-synaptic potential (IPSP), making it LESS LIKELY that the neuron will fire
Examples: serotonin
