Introduction to the nervous system Flashcards
What are the two parts of the nervous system?
CNS- central nervous system= brain and spinal cord
PNS- peripheral nervous system= spinal, cranial, visceral nerves and plexuses
The PNS is divided into two sections- what are they and describe their function
1) Somatic PNS = control motor and sensory function for the body wall (e.g. skin- sensory neurone), skeletal muscles (motor neurone in muscle)
2) Autonomic nervous system- things that you don’t think about. Regulates function of the viscera- internal organs, smooth (involunatry) muscle, pupils, sweating, blood vessels, bladder, glands, contraction of heart rate.
Autonomoic nervous system can be divided into 2 further sections:
Sympathetic and parasympathetic
Sympathetic- fight/flight
Parasympathetic- rest/digest
What is the difference between afferent and efferent axons?
Afferent axons- transmit towards the CNS
Efferent axons- transmit away from the CNS
Interneurones- CNS neurons that synapse with other CNS neurons within the brain and spinal cord
What are the 5 main structures of the brain (gross anatomy)?
Frontal- from the front (central gyrus)- responsible for personality and central conscious decision making
Parietal- sensory information from somatic nervous system
Occipital- visual cortex
Temporal- on the sides for auditory perceptions. Amygdala is there- it is responsible for what you are scared/ anxious about and your food/eating habits
Cerebellum- little brain- cognitive skills
Why does the brain have many folds?
It increases the surface area of the brain to pack in many neurones to process as much information as possible. Lower species like rats have fewer folds which is why they are not as advanced.
Describe the main structures in this picture
What are the 12 cranial nerves?
NB- cranial nerves control actions to do with the face and neck
- Olfactory I
- Optic II
- Oculomotor III
- Trochlear IV
- Trigeminal V
- Abducens VI
- Facial VII
- Vestibulocochlear VIII
- Glossopharyngeal IX
- Vagus X
- Accessory XI
- Hypoglossal XII
Pneumonic to remember it: Ooh, Ooh, Ooh, to touch and feel very good velvet. Such Heaven
What are the meninges?
The brain is covered in 3 layers for protection:
- Dura mater- outer layer (VERY STRONG). The dura mater has an inner and outer layer
- Arachnoid- the middle layer. There is also a subarachnoid space
- Pia mater- inner layer
The spinal cord and the CNS
The CNS ends at the margin of spinal cord. The dorsal and ventral roots emerge from the spinal cord and are a part of the PNS.
Ventral root- efferent pathway (autonomic)
Dorsal root- afferent pathway (somatic)
Describe the anatomy of neurones
Neurones have axons, dendrites and myelin sheath. Their length can vary depending on where they need to send a message to.
Remember that there are 4 different types of neurones
Describe spinal nerve anatomy
Spinal nerves contain afferent and efferent axons (it is like a 2 way street)
They are bundled into fassicles surrounded by perineurium
The whole nerve is in a tough epineurium capsule.
Individual axons are also wrapped with myelin and endoneurium, though some are unmyelinated, e.g. nociceptive (pain) neurons
NB when you get Dull pain- nonmyelinated neuone. Sharp pain- myelinated neurone
Synaptic transmission- describe action potentials briefly
Neurones communicate by changes in electrical activity. RMP= -70mV
Stimulus leads to VGSC opening and there is an influx of sodium. This is depolarisation.
VGKC opens and K leaves. This is repolarisation.
Neurotransmitters are released when the AP reaches the pre-synaptic terminal.
What are the other cells in the brain?
The ‘other’ cells (not neurones) are called glial cells (50%)
- Astrocytes- form the blood brain barrier and kepts the blood’s contents separate from the brain.
- Microglial- immune cells of the brain (macrophages)
- Oligodendrocytes (CNS)/ Schwann cells (PNS)- produce myelin sheath.
Describe the regeneration of neurones in the PNS
Axons in the PNS can regenerate after injury.
Injury leads to stimulation of phagocytes, which remove debris which would otherwise inhibit regrowth.
May be compromised by aberrant axon sprouting and non-specific target reinnervation- can lead to neuropathic pain- you will not get complete regeneration.
Regeneration of neurones in the CNS
They have limited regenerative capacity.
Glia exert inhibitory influence on regeneration- scars form in place of injured brain tissue
Absence of guidance cues that stimulate axon growth
What are the two pathways for sensory perception?
- Dorsal column-medial lemniscus pathway
Conveys fine touch, vibration and two-point discrimination
- Spinothalamic pathway
Conveys pain and temperature sensation
Describe the Dorsal column-medial lemniscus pathway
Nerve sensor from stimuli go to spinal cord (grey matter), send axons to the brain stem. The side switches. E.g if yous tubbed ur right toe, itd be the LHS. Then up to the primary somatosensory.
RHS of brain affects LHS body
LHS brain affect RHS of body
This is called contolateral movement
Describe the spinothalamic pathway
Enters the spinal cord but immediately switches to the otherside- does not wait to switch in the brain stem
Describe reflex action
Only need somatic input to the spinal cord and motor outputs from the spinal cord are required
NO NEED for communication with the sensorimotor cortex
Sensory and motor neurones going to and coming from the spinal cord must be intact
Describe conscious registering of sensation- action of nerves
Sensory inputs activated further sensory neurons in the grey matter of the spinal cord that transmit action potentials upwards to the sensorimotor cortex of the brain (ASCENDING tracts)
The sensorimotor cortex of the brain extend axons downwards to synapse with the spinal motor neurons and transmit action potentials for voluntary movement (DESCENDING tracts)
What are the two motor pathways
- Lateral corticospinal tract
- Vestibulospinal tract
