The Nervous System Flashcards
Outline the organisation of the nervous system
• central nervous system (CNS)
- made up of the brain and spinal chord
• peripheral nervous system (PNS)
- made up of nerves, efforts and receptors
- split into two different systems
–> somatic nervous system
- controls conscious activities e.g. running
–> autonomic nervous system
- controls unconscious activities e.g. digestion
Describe the structure and function of the hypothalamus
- the hypothalamus is found just beneath the middle part of the brain
- it controls the homeostatic mechanisms
- monitors the blood and regulates factors such as body temperature and blood water potential
- controls much of the endocrine function of the body as it regulates the pituitary gland through hormone control
Describe the structure and function of the cerebellum
- the cerebellum is underneath the cerebrum and it also has a folded cortex
- it’s important for muscle coordination, posture and coordination of balance
- receives information from various senses, retins, balance organs in the inner ear, joints and spindle fibres and sends impulses to the motor areas
Describe the structure and function of the cerebrum
- the cerebrum is the largest part of the brain
- it is divided into 2 hemispheres connected via the corpus callosum
- the cerebrum had a thin outer layer called the cerebral cortex which is highly folded
- the cerebrum is involved in vision, hearing, learning and thinking
Describe the structure and function of the medulla oblongata
- the medulla oblongata is at the base of the brain at the top of the spinal chord
- controls involuntary processes such as heart rate and breathing rate
Outline the organisation of the autonomic nervous system
• sympathetic nervous system
- most active during times of stress ‘fight or flight’
- the neurones of a pathway are linked at a ganglion just outside the spinal chord so pre-ganglionic neurones are very short
- post ganglionic neurones secrete noradrenaline as neurotransmitter
- causes increased heart rate, pupil dilation, increased ventilation rate, orgasm
• parasympathetic nervous system
- most active in sleep and relaxation
- the neurones of a pathway are linked at a ganglion within the target tissue so pre-ganglion neurones vary in length
- post ganglion neurones secrete acetylcholine as the neurotransmitter
- decreased heart rate, pupil constriction, decreased ventilation rate, sexual arousal
Describe the structure and function of a motor neurone
• the motor neurone has a cell body at the end with a large nucleus and lots of RER and Golgi bodies
• it has a many short dendrites that carry imposes to the cell body
• a long axon which caries an impulse from the cell body to the effector
- They carry the Action Potential from the CNS to the Effector
Describe the structure of a sensory neurone
- the sensory neurone has long processes on either side of the cell body
- a dendron carrying nerve impulses from a receptor to the cell body
- an axon carrying an impulse from the cell body to the effector
- they are transducers and convert the stimulus into a nerve impulse
- they carry the action potential from the Sensory Receptor to the CNS
What is the difference between a sensory neurone and a motor neurone?
In the Sensory Neurone, the DENDRON is called the AXON after the Cell Body.
(It’s only called the AXON AFTER the Cell Body)
Cell Bodies of Motor Neurones are located in the CNS or Brain - (At the end of the Neurone)
Cell Bodies of Sensory Neurones are located around the body - (In the MIDDLE of the Sensory Neurone)
What is the reflex arc?
Change in environment
⬇️
Stimulus
⬇️
Detected by Sensory Receptor
⬇️
Action Potential sent along sensory Neurone⤵️ (To Brain) ⬇️
⬇️ CNS➡️Brain +Spinal Cord◀️⬇️
Action Potential sent along Relay Neurone ⬇
⬇️ (Synapse) ⬇️
Action Potential arrives at Motor Neurone ↩️
⬇️
Signal passed to Effector (Muscle/Gland)
⬇️
Effector Responds
Describe how resting potential is established
- when not conducting an impulse the potential difference across the membrane is about -70 mv
- the outside of the membrane is positively charged compared to the inside so the membrane is polarised
- sodium-potassium pumps actively transport (need ATP) 3 Na+ ions out of the neurone for every 2K+ ions moved in
- the membrane is impermeable to sodium ions so they can’t diffuse back in which creates a sodium ion electrochemical gradient because there are more positive sodium ions outside the cell than inside
- the membrane is permeable to potassium ions so they diffuse back out through potassium ion channels using facilitated diffusion down their concentration gradient
- this makes the outside of the cell positively charged compared to the inside
Describe how an action potential is generated
- the membrane is at resting state, -70 mv inside compared to the outside so it is polarised
- the sodium ion channels open and the membrane becomes more permeable to sodium so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient
- this makes the inside of the neurone less negative and reaches the threshold potential of around -50 mv (it is depolarised)
- this causes voltage-gated sodium ion channels to open and many Na+ ions diffuse into the neurone
- the potential difference across the membrane reaches +40 mv so the inside is now positive compared to the outside
- this causes sodium ion channels to close and voltage gated potassium ion channel to open
- the membrane is more permeable to potassium ions so they diffuse out of the neurone down the potassium ion concentration gradient, this starts to bring the potential difference back towards the negative resting potential (repolarisation)
- potassium ion channels are slow to close so there’s a slight overshoot where too many potassium ions diffuse out of the neurone, this causes the potential difference to become more negative than the resting potential (hyperpolarisation)
- the ion channels are then reset and the sodium-potassium pump returns the membrane back to its resting potential
Describe and explain how an action potential is transmitted in a myelinated neurone
- No Na+ ions can diffuse into the axon where Schwann cells are
- There are open voltage gated Na+ ion channel at each node of ranvier (gap between Schwann cells)
- So the action potential ‘jumps’ from mode to node
- This is known as saltatory conduction
Describe the transmission of an action potential across a synapse
- an action potential arrives at the synaptic knob of the presynaptic neurone
- this triggers the voltage-gated calcium ion (Ca2+) channels to open on the presynaptic membrane so that Ca2+ ions can diffuse into the cell
- the influx of Ca2+ ions causes vesicles containing acetylcholine within the neurone to move to the cell surface membrane and fuse with the presynaptic membrane
- via exocytosis, the vesicles release the acetylcholine into the synaptic cleft which diffuses across the gap down the concentration gradient to reach the postsynaptic membrane
- the acetylcholine binds to receptors on sodium ion (Na+) channels on the membrane which causes the channels to open, so Na+ ions diffuse into the cell
- the influx of sodium ions triggers an action potential, via the depolarisation of the membrane, on the postsynaptic membrane which travels along the membrane of this new neurone
Describe the structure and function of the spinal cord
- it is a an extension of the central nervous system
- it is responsible for transmission of nerve impulses from the body to brain and vice versa
- it is protected by meninges, contain CSF and by the bony vertebrae of the spinal column
