CNS Flashcards
What gives rise to higher complexity and higher computing functions
The number of folds, not the size of the brain
The number of neurons in the cortex
Morphology is strictly correlated with function.
Describe the communication of the CNS with the outside world
somatic and special senses
Describe the communication of the CNS within the organism
visceral sensation,
involuntary movement,
somatic movement,
higher cognitive functions
What is meant by an effector
Effectors are target organs whose response change according to neural commands.
What is meant by a receptor
Sensory structures that detect changes in the internal and external environment.
What does dorsal and ventral mean in the brain
Dorsal- superior
Ventral- inferior
What does rostral and caudal mean in the brain
Rostral- towards frontal lobe
Caudal- towards the spinal cord.
What is the spinal cord enclosed in
The spinal cord is enclosed and protected by the vertebral column.
What does the vertebral column permit
Movement
Describe the location of the spinal cord
The spinal cord occupies the vertebral canal within the vertebral column and is continuous rostrally with the medulla oblongata. The cord is approximately cylindrical and arranges segmentally with a central cellular area (grey mater) surrounded by nerve-fibre tracts (white mater). The tracts carry information between different levels of the spinal cord (thereby permitting reflex reactions) and also to and from supraspinal structures.
Where are the horns found
Within the grey mater
Describe the structure of the spinal cord
▪ The spinal cord is a column of neural tissue which is segmental.
▪ Each segment has a pair of spinal nerves attached to it.
▪ The core consists of grey matter (mainly neuronal soma).
▪ There is a wrapping around of the white matter (contains axons).
▪ The grey matter is then divided into sensory and motor areas.
Where do the dorsal and ventral roots join to form spinal nerves
Near to the intervertebral foramen where spinal nerves exit the vertebral canal.
Describe the intervertebral foramina
Along the sides of the vertebral column, you have a series of holes called intervertebral foramina (with each of these foramina having a spinal nerve coming from them).
Where does the spinal cord end
▪ The spinal cord is MUCH SHORTER than the vertebral column. o This is because the spinal cord finishes growing earlier in development compared to the vertebral column.
The spinal cord terminates at the level of the intervertebral disc between L1/L2 in adults
What is the consequence of the spinal cord being shorter than the vertebral column
A lumbar puncture can be inserted into the subarachnoid space below this level to take a sample of the CSF without damaging the spinal cord.
o LPs are usually taken between L3 and L4.
The area with no spinal cord is called the lumbar cistern.
What exists below the termination of the spinal cord
The area with no spinal cord but a flurry of nerves is also called the Cauda Equina.
The Cauda Equina are descendents of the lumbar and sacral nerve roots.
What are the different levels of the vertebral column
▪ Cervical – C1-C7 → 7 vertebrae.
▪ Thoracic – T1-T12 → 12 vertebrae.
▪ Lumbar – L1-L5 → 5 vertebrae.
▪ Sacral – S1-S5 → 5 vertebrae (varies)
What does each spinal cord segment innervate
A particular skin area (dermatome) and muscle area (myotome)
Why does white mater appear white
Due to the myelination of the axons
Where are the two enlargements of the spinal cord found
The diameter of the spinal cord is not the same along its length.
The spinal cord has two enlargements- the cervical (C3-T1) and lumbar (L1-S3)- which provide innervation to the upper and lower limbs respectively
Describe the structure of the grey mater of the spinal cord
Cells in the central grey mater can be divided into a series of layers in the dorsal horn and as a series of columns in the ventral horn. These layers and columns are known as Rexed’s laminae (numbered I-X) and are based on groupings of similarly shaped bodies
Dorsal Horn
Ventral Horn
Intermediolateral column
Describe the dorsal horn of the grey mater
The dorsal horn layers are involved in sensory pathways and are the target sites for some sensory afferent nerves, particularly for pain, temperature and crude touch.
Describe the ventral horn of the grey mater
The ventral horn columns are made up of pools of motor neuron innervating skeletal muscle. Medial motor neurons supply proximal muscles, and lateral motor neurons supply distal muscles.
Describe the intermediolateral column of the grey mater
Where the cell bodies of preganglionic sympathetic neurons are found.
Describe the structure of the white mater
The white mater of the spinal cord consists of ascending and descending nerve fibres and completely surrounds the grey mater. As a general rule. the ascending sensory tracts run at the periphery and the descending motor tracts occupy a more central position.
What is the relationship between the vertebrae and the number of spinal nerves
There is an equal number of nerves and vertebrae EXCEPT there is an extra nerve above C1 so there are 8 cervical nerves.
Hence there re 31 pairs of spinal nerves.
Describe the relationship between the vertebrae and the direction of the spinal nerves
C1-C7 exit the vertebral canal above the first seven cervical vertebrae. C8 exits below the 7th cervical vertebrae, the remainder exit below their corresponding vertebrae,
Describe the functions of the spinal cord
Connects the PNS and ANS to the brain
Carries sensory signals to the brain
Carries motor signals to the muscles
Coordinates reflexes
Describe the patellar reflex
Hitting patella tendon stretches the quadricep (detected by stretch receptors)- impulse sent to spinal cord via dorsal root. Reaches cell bodies of motor neurons in grey mater, which innervate the quadricep and hamstring, results in contraction of the hamstring.
Describe the embryonic classification of the brain
Forebrain, midbrain and hindbrain
Describe the more functional classification of the brain
Cerebrum
Cerebellum
Diencephalon (thalamus and hypothalamus)
Brainstem (midbrain, pons, medulla oblongata)
How many cranial nerves have their origin in the brainstem
10
Describe the function of the cell bodies of the cranial nerves found in the brainstem
Responsible for the control of many vital functions such as: breathing, heart rate, blood pressure, swallowing, balance etc.
Responsible for defensive reflexes (cough, gag, sneeze…)
Involved in sleep-wake cycles, alertness and consciousness
Describe the link between the midbrain and Parkinson’s disease
Midbrain includes the substantia nigra which degenerates in Parkinson’s Disease
Describe the brainstem
All sensory and motor fibres that connect the cerebrum, the cerebellum and spinal cord run through it
Contains the nuclei of 10 of the cranial nerves (III to XII)
Describe the pyramidal decussation found in the medulla oblongata
Corticospinal fibres crossing over to form contralateral corticospinal tract
Describe reticular formation
Once all the nuclei and tracts have been identified in the brainstem, a central core of cells remains. This loosely arranged network is called the brainstem reticular formation.
▪ The reticular activating system controls the level of consciousness.
What is the pons also connected to
The cerebellum.
Describe the functions of the brainstem
Medulla controls vital functions eg. respiration
Cranial nerves supply motor, sensory and autonomic innervation to the head
Ascending and descending tracts connect the spinal cord with the forebrain
Reticular activating system controls the level of consciousness
Describe the structure of the thalamus
Bilateral- exists on both sides of the brain
In the middle is the 3rd ventricle.
It is shaped like a rugby ball.
Describe the function of the thalamus
relays information between cerebral cortex and lower structures
integration centre for somatic and special senses information and projection to cortex. Involved in emotional status, consciousness, appropriate motor response.
Describe the hypothalamus
Hypothalamus – Controls homeostasis. o Interfaces between the limbic system, ANS and endocrine system. o Found below the thalamus.
Describe the functions of the hypothalamus
Associated more with the viscera
integration hub. Regulates temperature, hunger, thirst, hormone (connected with pituitary) and autonomic function
Describe the influence of the thalamus on cortical processing
The thalamus acts as a gateway to the cortex for sensory information and its output to the cortex can be modified, such as by the brainstem reticular activating system. The thalamus, can, therefore, exert considerable influence on cortical processing
What are groups of cell bodies in the CNS called
Nuclei, with the exception of the basal ganglia.
Describe the basal ganglia
Basal Ganglia – group of nuclei which produce the pattern of movement and work together with the motor cortex.
Where is the basal ganglia found
Found deep inside the cerebral cortex and is one of the main nuclei.
Describe the caudate and putamen
The caudate and putamen contain identical cell types and together they form the main cortical target input to the basal ganglia: the corpus striatum. The striatum receives somatotopic information from motor, sensory, association and limbic areas as well as the intralaminar nuclei of the thalamus (connected to cortex, thalamus, nigra).
Putamen- motor control
Caudate- eye movements and cognition.
Describe the putamen and Globus pallidus
Form the lentiform nucleus
The Globus pallidus is the output source to the thalamus.
List the parts of the basal ganglia
Caudate Putamen Globus pallidus Subthalamic nuclei Substantia nigra
Describe the functions of the basal ganglia
Control of movement:
facilitating voluntary movement, inhibiting unwanted or inappropriate movements, “fine tuning”
Describe the fissures in the cerebral cortex
Deeper ridges than sulci
Longitudinal fissure- divides the two hemispheres
Central fissure- separates the frontal and parietal lobe
Lateral fissure- separates temporal lobe from frontal and parietal lobe.
Fissure are the same in everyone
Sulci are as individual as the fingerprint.
Describe the dimensions of the cortex
2-4 mm thick
~30% exposed
70% within sulci
How many functional and histologically distinct areas are there in the brain
47
Describe the two types of cortex in the hemisphere
Primary cortical areas- basic functions occur here, they are small and discrete.
Association cortex- the rest of the cortex- higher-order functions take place in these regions.
Which areas form the primary cortical area
Broca's area Wernicke's area Primary motor cortex Primary auditory cortex Primary somatosensory cortex Primary visual cortex
Describe the primary motor cortex
Found in the frontal lobe
Initiates movement. The neurons send signals for fine, precise coordinated limb movements (contralateral)
▪ Sends axons down descending pathway to stimulate motor neurones in spinal cord → PNS. ▪ Has a somatotropic (arranged like a body map, i.e. head controlled by bottom of area, legs controlled by top of area) arrangement. → damage corresponds to a place.
Describe the primary somatosensory cortex
Found in the parietal lobe
▪ Adjacent to the motor cortex. ▪ Also has a somatotropic arrangement. ▪ Receives general sensory information.
Describe the primary visual cortex
Found in the occipital lobe
▪ Receives information (visual signals) from the retina
Describe the primary auditory cortex
Found in the temporal lobe Receives information (auditory signals) from the ears.
Describe Broca’s area
Found in the frontal lobe- left hand side
The muscle movements that articulate speech are determined here before being sent to the bulbar muscles via the cranial nerves.
Describe Wernicke’s area
In the dominant hemisphere- left, the auditory association cortex is known as Wernicke’s area. This is where language comprehension and responses occurs.
Describe the somatosensory association area
it interprets the sensory information to make cognitive sense of it (hand-eye coordination)
Describe the motor association area
It is where the neurons plana program for the contraction of muscles required for certain actions.
Describe the visual association area
It recognises faces and other objects
Describe the auditory association area
It recognises the signals received as spoken words, a familiar piece of music, a voice
Describe the primary gustatory cortex
It receives gustatory (taste) signals.
Describe the prefrontal cortex
It gives us sense to our relationship with the world, enabling us to think about it and execute appropriate behaviour (mood, personality)
Describe the laminar structure of the cortex
6 layers- neocortex.
Some layers- cells only (pyramidal neurons)
Some layers- only have connecting white mater and fibres
Older cortex (hippocampus)- 3/4 layers
What are the roles of the limbic system
motivation,instinctive behaviour,emotion,memory
Describe the limbic system
Complex system of fibre tracts and grey mater. Lies in the medial aspect of each temporal lobe, encircling the upper part of the brainstem. Components in the diencephalon: Hypothalamus Mammillary body Amygdala Anterior group of thalamic nuclei
Components in cortex:
Cingulate gyrus
Hippocampus
Parahippocampal gyrus
Where is the cerebellum located
Found towards the back of the brain and below the cerebral hemispheres.
Attached to the brainstem posteriorly, by 3 pairs of peduncles
Describe the structure of the cerebellum
Grey cortex (with deep parallel folds, folia), deeper white matter, with nuclei. Two hemispheres divided in lobes, central vermis Folia- increase surface area
Describe the functions of the cerebellum
It doesn’t initiate movement but it coordinates movement and is important for learning new motor skills such as riding a bike or playing the piano.
vestibular system for balance
spinal cord and muscles of locomotion, posture; muscle tone
Motor cortex and thalamus for learned movements (eg manual skills, trajectory, timing, speed and force)
Diseases that affect the cerebellum manifest with ataxia.
Describe the white matter in the brain
The white matter connects the different parts of the brain
Commissural fibres- connect the two hemispheres (Corpus callosum)
Association fibres- connect different regions within the hemispheres
Projection fibres- verical (cortex to spinal cord). Sensory fibres from spinal cord pass between lentiform nucleus and thalami (internal capsule) and fan out as corona radiata
Describe the base of the skull
Anterior cranial fossa- frontal lobe
Middle cranial fossa- Temporal lobe, pituitary gland, hypothalamus
Posterior cranial fossa- Brain stem, cerebellum.
Describe the two layers of the dura mater
Periosteal- connected to the bone of skull.
meningeal layer- connected to the lower meninges
In between, some areas, space where venous blood collects (sagittal sinus).
Describe the structure of the meninges
- Dura mater – Tough membrane attached to bone or forming partitions (Dural folds) with venous sinuses in their margins.
- Arachnoid membrane – Thin membrane attached to underside of the Dura. Holds the blood vessels in space
- Pia mater – Delicate membrane closely adherent to the surface of the brain and spinal cord.
Where do the blood vessels run
In the sub-arachnoid space
What does the dura follow
The fissure, pia mater is more flexible and can follow the sulci.
Describe the sub-arachnoid space
▪ Between the arachnoid and the pia, you have the sub-arachnoid space where the CSF circulates. ▪ There are venous sinuses over the surface of the brain which are occasionally penetrated by protrusions of arachnoid membrane that allow the reabsorption of CSF – These are arachnoid villi.
Describe the ventricular system
▪ There are TWO (one in each hemisphere of the brain) large C-shaped ventricles with a spur at the back, these are the lateral ventricles. ▪ The two lateral ventricles, via a tiny foramen, join up with a single midline ventricle (interventricular foramen) called the 3rd Ventricle located in the middle of the diencephalon. ▪ At the base of the 3rd ventricle, there is a narrowing to form a fine channel called the cerebral aqueduct. ▪ The aqueduct passes through the midbrain and at the top of the midbrain it opens up again into a tent-shaped 4th ventricle. ▪ The pons and medulla is in front of the 4th ventricle and the cerebellum is behind it. ▪ At the lower part of the medulla, the 4th ventricle narrows again to form a very fine channel called the central canal which goes down the spinal cord.
What do all ventricles have
The choroid plexus- where CSF is made- they are vascular structures
Describe the composition of the CSF
▪ Produced by ependymal cells found in the ventricles called the choroid plexus. ▪ The choroid plexus filters the blood, takes out most of the cells and then secretes it.
Composition similar to plasma (high Na+, low K+) but:
Lower glucose (2/3)
Much lower protein (200x)
Lower Ca2+, K+
Higher Cl-, Mg
Slightly lower pH (7.33)
Fewer cells
In equilibrium with ECF of brain and so can be diagnostic.
Describe the volume and flow rate of the CSF
▪ Volume = 150ml (turned over 3-4 times a day) ▪ Flow rate = 500ml/day
What are the functions of the CSF
▪ To cushion the brain within the skull by acting as a shock absorber. ▪ To circulate nutrients and chemicals filtered from the blood. ▪ To remove waste products from the brain.
Immune cells
Remove waste
Describe the circulation of the CSF
▪ CSF then circulates through the ventricular system and gets to the 4th ventricle which has holes in it so the CSF can exit the 4th ventricle and spread across the outside of the brain. ▪ The CSF can then circulate in the sub-arachnoid space between the meninges. ▪ It is then reabsorbed into the venous system by arachnoid villus.
One-way direction for turnover.
