Nervous system structure Flashcards
What brain axes is in the direction of the nose?
Rostral
What brain axes is pointing to the top of the head?
Dorsal
What brain axes is pointing to the back of the neck in the brain stem?
dorsal
What are the middle and sides of the brain called?
Medial and lateral
How man cranial nerves are there?
12
What is the PNS?
The 12 cranial and 31 spinal nerves that come out at each vertebrae
How do the dorsal and ventral parts of the spinal cord differ in the information they carry?
Dorsal is afferent
Ventral is efferent
What are the two tracts of the afferent PNS and how do they differ?
Spinothalamic and dorsal column
The spinothalamic tract carries pin prick, temperature, and light touch sensations
The dorsal column tract carries two-point sensitivity, vibration, and propioception
What are the two parts of the autonomic nervous system and how do they differ?
Sympathetic and parasympathetic
Sympathetic have nerves coming all over the spinal cord and ganglia are near vertabrae
Parasympathetic = all nerves come from either the top (brain stem) or the bottom (S2-4) and ganglia are found near target organ
How does the CNS develop?
From a neural tube it expands and folds to form the brain.
What is the grey matter in the brain stem?
cell bodies
What is the white matter in the brain stem?
Myelinated axons
Where is the dorsal column tract in the spinal cord and what parts is it made up of?
It is in the dorsal, medial part of the spinal cord and is made up of the Cuneate and Gracile
Where is the spinothalamic tract in the spinal cord?
It is in the front (ventral) half of the spinal cord.
Where do the two afferent PNS tracts cross?
The dorsal column tract crosses at the brain stem while the spinothalamic tract crosses immediately after entering through the dorsal horn and stays on the other side until reaching the brain.
In general nerves in the back tends to cross higher in the brainstem
What is the PNS tract containing the motor neurons called?
Corticospinal tract
Where is the corticospinal tract and where does it cross?
95% of the motor fibers travel in the lateral spinal tract.
They cross in the brain stem and travel out through the ventral root after passing through the spinal column.
The other 5% are in the anterior corticospinal tract and these are in the ventral side and cross over in the spinal cord
What is the purpose of the anterior corticospinal tract?
It acts as a safety net to retain some amount of movement in case of damage to the lateral corticospinal tract
What happens if I stab someone in the right side of the spinal cord?
The right Gracile and Cunaete are damaged, so they feel no two-point sensitivity, vibrations, or propioception in the right side of the body.
The right spinothalamic tract is affected so they feel no pinprick pain or temperature (light touch is a bit mixed) on the left side of their body
Also the lateral corticospinal tract on the right is damaged so movement on the right side of the body is impaired (but not totally because of the anterior corticospinal tract on the left)
What are the 3 sections of the brainstem?
Midbrain
Pons
Medulla
What are the 3 things contained by the brainstem?
Grey matter is organised as 12 nuclei (one for each nerve)
White matter has the same tracts in the spinal cord going up and down
The reticular formation
What is the reticular formation?
Regulates consciousness, pain perception, cardiovascular and respiratory centres.
Why are strokes in the brain stem so bad?
Because they can damage the reticular formation and then this leads to brainstem death
What is the cerebellum and where is it?
It is under the occipital lobe and it controls balance and coordination
Explain the parts of the cerebellum and what they control
The medial portion controls the trunk while the lateral portions control the arms and legs
The cerebellum is the only bit of the brain that does not cross over (right side controls right body)
What is the diencephalon
The caudal (posterior) part of the forebrain, containing the epithalamus, thalamus, hypothalamus, ventral thalamus, and the third ventricle.
What did people use to think the thalamus was like?
They thought it was like a train station because it takes all the nerves from the dorsal columns and spinothalamic tract
Why is the thalamus not like a train station?
It is involved in gating off pain perception (makes pain worse when you feel bad and less pain when eg. running from gunman)
Involved in consciousness
Functions:
•Determines which sensory information reaches the cortex
•Links basal ganglia with the cortex
•Like the reticular formation, it influences attention and consciousness
What does the hypothalamus do?
It is the kingpin of the endocrine system with a pituitary henchman
Name the lobes of the cortex and what they do
Frontal lobe:
a) Prefrontal cortex:Personality, value judgement, control urges, movement
b) Primary motor cortex: Executes motor programme
c) Secondary motor (association) cortex: Premotor area, supplementary motor area. Stores learned motor activity, plans programs of activity for the primary motor cortex.
Parietal:
a) Association sensory area (integrates all the sense info -eg. putting together voice with the image of someone’s face)
b) Primary somatosensory area
Occipital: Vision (primary and secondary visual cortex: see and recognise it)
Temporal: Sound (primary and secondary cortex)
Describe the sensory humunculus
Different body parts are disporportionately represented (sensitive).
The order from the interhemispheric fissure outwards: legs –> arm –> face
Why might one say that one hemisphere is dominant and why is this wrong?
Because the first few important functions are done in the left hemisphere but there are loads of important functions done by the right.
Lesions to right side are more funcitonally impaired because they are not aware of it
What percentage people are left hemisphere dominant?
99% (all right handers and 50% of left handers)
What are the left and right hemispheres specialised in?
Left: calculations, in charge of speech/language, logic (called dominant because easier to assess)
Right: interspacial orientation, complex tasks and thinking
What are the components of the limbic system?
- Subcallosal gyrus
- Cingulate gyrus
- Parahippocampal gyrus
- Hippocampal formation
- Amygdala
- Mamillary bodies
- Anterior thalamus
Where is the limbic system?
In the brain encircled by ventricles
What does the cingulate gyrus do?
It passes info from the inner to the outer portions of the limbic system
What are the parts of the basal ganglia?
- Caudate
- Putamen
- Globus pallidus
What are the basal ganglia?
Group of nuclei with an important role in control of posture and voluntary movement
Frontal cortex asks it permission
Where do the basal ganglia get their input?
Afferents from cortex, thalamus and brainstem, including the substantia nigra.
Where do basal ganglia outputs come from
Output from globus pallidus influences motor activity.
What does the hippocampus do and what effect does damaging it have?
Converts recent memory to long term memory.
Lesions can result in anterograde amnesia (Korsakoff’s). Damage to the hippocampus is also associated with alzheimers (no long term memory)
What part of the brain is affected in HD?
The basal ganglia
What is the purpose of the limbic system?
Emotion, behaviour, drive and memory.
Explain the idea of dominance
Certain functions are predominantly performed in one hemisphere.
Describe the general structure of the brain
Two hemispheres separated by the longitudinal fissure
Corpus callosum connects the hemispheres across the midline.
Surface area of cortex is increased by folds (gyri) separated by fissures (sulci).
Divided into 4 lobes by sulci (central, parieto-occipital, lateral, calcarine).
Describe PNS organisation
12 pairs of cranial nerves and 31 pairs of spinal nerves
Each spinal nerve is connected to the cord by two roots.
•Ventral root
•Dorsal root
The roots unite to form spinal nerves which innervate our muscles and skin.
What types of spinal nerves are there?
8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
Name the 5 types of sensory receptors and what they do
- Mechanoreceptors -Mechanical deformation.
- Thermoreceptors- Cold, heat.
- Nociceptors- Stimuli damaging tissue
- Electromagnetic receptors- Light (rods, cones)
- Chemoreceptors- Chemical changes
What 2 parts are the CNS made up of?
Brain, spinal cord
Describe the general anatomy of the spinal cord
- Two halves separated by dorsal and ventral median fissures
* Central canal
Where does the cerebellum get inputs from?
Cerebral cortex
Proprioceptive sensory information
Vestibular nerve
What is the gross anatomy of the cerebellum
Two hemispheres joined by vermis
Connected to the posterior aspect of the brainstem by three peduncles (superior, middle, inferior).
Cortex: Outer covering of grey matter.
Nuclei: Three masses of grey matter embedded in the white matter. The main output of the cerebellum.
Which sensory infomation bypasses the thalamus?
Olfactory
