CNS Flashcards
What is the main function of the CNS?
Communication!
- With the external environment- somatic and special senses, mainly through the PNS
- Communication within the organism- visceral sensation, involuntary movement, somatic movement, higher cognitive movement
What makes one species’ brain more complex than another species’?
The number of folds (gyri and sulci) that the brain has (i.e. the surface area of the brain when you stretch it out)
It’s not the size of the brain nor the number of neurones inside the brain.
What is the spinal cord?
It is a column of neural tissue which is segmental.
Each segment has a pair of spinal nerves attached to it.
What is the vertebral column?
The spinal cord lies in the vertebral canal in the vertebral column. Along the sides of the vertebral column you have a series of holes called intervertebral formamina- the foramina have the spinal nerves coming out of them
What is inside the segment of the spinal cord?
The core= grey matter (contains neuronal cell bodies)
The axons have white matter around them (i.e. white matter around the grey matter)
The grey area is split into sensory (dorsal) and motor (ventral) areas.
Dorsal= towards the CNS
Ventral= away from the CNS
Spinal nerve= both ways
Describe the levels of the spinal cord levels (number in each level)
There are 31 pairs of spinal nerves:
Cervical- 7 segments on vertebra, 8 nerves (extra one above c1)- nerves above vertebrae
Thoracic- 12 segments, 12 nerves (nerves below vertebrae)
Lumbar- 5 segments, 5 neves (nerves below vertebrae)
Sacral- 5 segments, 5 nerves (nerves below vertebrae)
Coccyx- 1 segment, 1 nerve (tail end) (nerves below vertebrae)
Describe this picture wrt dorsal and ventral horns
Dorsal horn- sensory area cells receive sensory recieve sensory information via spinal nerves.
The cell bodies of these sensory neurones are in the dorsal root ganglion
The axon continues by the dorsal root and enters the dorsal horn. The info is taken up the ascending tract to the brain’s white matter.
Ventral part of the grey matter= motor neurones. Axons of the motor neurones go out of the ventral roots and to the muscles.
The difference between the spinal cord and vertebral column
The spinal cord is infront of the vertebral column.
The spinal cord is shorter than the vertebral column as it finishes growing earlier in development and the vertebral column continues to grow.
The lumbar and sacral segments are considerably above the vertebrae where the spinal nerves have to come out.
Parts where there an no spinal cord- lumbar cistern. It contains CSF. Lumbar puncture between L3 and L4 to collect this CSF.
Bit where there is no spinal cord but a flurry of nerves= cauda equina
What are the functions of the spinal cord?
- Connects the peripheral and autonomic nervous system to the brain
- Carries sensory signals to the brain
- Carries motor signals to the muscles
- Coordinates reflexes
Give an example of a reflex
Patellar reflex
Stretching of muscle is sensed by stretch receptor- reflex to motor neurone to serve that muscle. Keeps us balanced.
What is the cerebral cortex?
The deeply folded area of the brain.
Deep inside the cerebral cortex there are lots of nuclei (neurones)
One of the main nuclei is the basal ganglion- the basal ganglia is the main group of nuclei that produce the pattern of movement and work together with the motor cortex.
There are different lobes: frontal, parietal, temporal and occipital
What is the corpus callosum?
The bendy bit of white matter in the middle- mainly consisting of axons.
The corpus callosum interconnects corresponding areas of the 2 hemispheres so there is a constant conversation between the 2 hemispheres.
The diencephalon is directly underneath the corpus callosum
What is the diencephalon?
The diencephalon is strongly attached to both hemispheres
Consists of the thalamus (which is superior to) and the hypothalamus.
Thalamus- higher area of the diencephalon- it is a relay station for information going inbetween the cerebral cortex and the other parts of the CNS (in both directions)- it is the integration hub. Regulates temperature, hunger, thirst and autonomic function
Hypothalamus- important for coordinating homeostasis. Integration centre for somatic and special senses information and projection to cortex. Involved in emotional status, consciousness and appropriate motor response.
Optic chiasm- place where nerve fibres from half of each retina cross over.
Pituitary gland- production of hormones
What is the brain stem?
Underneath the diencephalon, is the midbrain. Midbrain has the substantia nigra which degenerates in parkinson’s disease.
The pons is inferior to the midbrain and it has an anterior bulge
Attached to the bottom of the pons is the medulla which merges with the top of the spinal cord as it descends through the base of the skull.
The brain stem also contains a number of nuclei which control our vital functions (respiratory centre/ cardiac centre)- nuclei= group of neurones- has nuclei for 10 cranial nerves.
There are ascending and descending pathways in the brain stem- ascending is sensory information, descending comes down from motor corticol areas down the brain stem.
Cranial nerves are attached to the brain stem. These provide motor and sensory innervation for the head region (hearing and vision)
What does the cerebellum do?
It has motor function- does not initiate movement but it coordinates it.
It is important for learning motor skills.
Connected for muscle memory on actions- learns actions you do over and over again.
Problems lead to ataxia.
It is attached to the brainstem posteriorly by 3 pairs of peduncles.
Cerebellum= grey cortex, deeper with white matter and nuclei. 2 hemispheres divided in lobes, central vermis.
The brain can be split up into 3 main parts- what are they?
What are the cerebral hemispheres?
- The cortex
- Basal ganglia
What is the basal ganglia?
Structure linked to the thalamus at the base of the brain and involved in control of movement. It facilitates voluntary movement, inhibiting unwanted or inappropriate movements (fine tuning)
- Caudate + Putamen = Corpus Striatum - connected to cortex, thalamus, nigra
- Putamen + Globus Pallidus= Lentiformnucleus
Cortical areas- what are the 2 types of cortex?
- Primary cortical areas- small and discrete areas
- Association area
What is the primary motor cortex?
Primary motor cortex- the neurones send signals for precise, finely coordinate limb movements. The cells send axons down through the descending pathway to stimulate motor neurones in the spinal cord- the spinal motor neurones will stimulate the muscle via the PNS. It has a somatotopic arrangement (arranged like a body map- area at the bottom controls movement of head, middle is movement of arms and top is movement of the legs- upside down man)
If there is damage to the primary motor cortex, there will be loss of voluntary movement somewhere.
Cerebral hemisphere has contralateral effects- what does this mean?
Opposite side to the side of the brain affected is affected
What does the somatotopic arrangement of the cortex mean?
It is arranged like a body map
Area at bottom- controls movement of head
Middle bit- controls the movement of the arms
Top area- controls the movement of legs
What is the arrangement of tissues in the cortex?
Laminar arrangement.
The outer neural sheet covering the cerebral hemisphere can be described to be laminar due to arrangement of the cortical neurones into 6 distinct layers.
What does the primary somatosensory cortex do?
It receives general sensory information coming from the body- e.g. touch, pain and temperature
It is adjacent to the primary motor cortex and it has a somatotropic arrangement too.
What does the primary auditory cortex do?
It receives auditory signals from the ears
What does the primary visual cortex do?
First to receive visual signals from the retina
What are association cortex areas?
They are cortical areas that are NOT primary cortex
They are places where a higher function takes place- like learning, perception and thinking
E.g. Wernicke’s Area- important for understanding language
Broca’s area- important for speech
What is the limbic system?
The limbic system is made up of different parts of the brain but with common function.
Corpus Callosum, formix, pineal gland etc.. They are all connected and control emotion and instinct behaviour. Needed for memory and motivation.
Which structures are connected to the cerebellum for its function?
- Vestibular system for balance (sensory system)
- Spinal cord and muscles of locomotion, posture and muscle tone
- Motor cortx and thalamus for learned movements (e.g. manual skills, trajectory, timing, speed and force)
What is the cranium?
It is another word for the skull.
Anterior fossa- holds the frontal lobe
Middle fossa- holds the temporal lobe
Posterior fossa- holds occipitial lobe
Foramen magnum- hole in the cranium where the brainstem descends
What are the meninges?
They lie inbetween the brain and bone. They lie in the following order:
- Dura mater
- Arachnoid mater
- Pia mater
Subarachnoid space in between the arachnoid and pia mater where CSF circulates.
Describe the ventricle system
There are 2 C shaped ventricles with a spur at the back (one in each side hemisphere)- blue
They are the lateral ventricles.
The 2 lateral ventricles join up with a single midline ventricle called the 3rd ventricle (yellow). The interventricular foramen connects them together.
3rd ventricle is in the middle of the diencephalon. The base of the 3rd ventricle narrows to form a cerebral aqeuduct (red)
The cerebral aqueduct passes through the midbrain and it opens up again into a tent shaped 4th ventricle (purple)
The pons and medulla are infront of the 4th ventricle and the medulla is behind it.
The 4th ventricle begins to narrow again to form a very fine channel= central canal (green) which goes down into the spinal cord.
What is Cerebrospinal fluid (CSF)?
It is produced by the choroid plexus (ependymal cell found in the ventricles).
The choroid plexus filters out the blood, takes most of the blood out and secretes it.
CSF circulates through the ventricular system and gets to the 4th ventricle. The 4th ventricle has holes and the CSF can exit and spread in the brain.
Where does CSF circulate in the brain?
It circulates in the sub-arachnoid space between the meninges.
It is reabsorbed into the venous system by the arachnoid villi.
The arachnoid membrane has outpockets which push through the wall of the venous sinus and allows reabsorption of CSF
What is hydrocephalus?
Blockage causing build up of CSF in the brain.
Mainly tumours in the aqueduct as it is very thin.
CSF composition vs normal plasma
CSF has
- higher Na and lower K
- Lower glucose
- Much lower protein
- Lower Ca,
- Higher Cl and Mg
- Slightly lower pH
There’s around 150ml total but the choroid plexus produces around 500ml a day
Function of CSF?
- Cushioning
- Nutrition
- Removing waste
- Immune cells
