Human Brain Flashcards
What are the 4 main lobes of the brain?
Temporal, Occipital, Frontal and Parietal
What divides the brain into its hemispheres?
The longitudinal fissure
What are sulci/fissures/gyri?
Sucli are shallow grooves in the brain’s cerebral cortex.
Fissures are deep grooves in the brain’s cerebral cortex
Gyri are the ridges between them.
What divides the frontal and parietal lobes?
The central suclus
What divides the frontal and temporal lobes?
The lateral fissure
What divides the temporal/parietal and occipital lobes?
The Parieto-occipital sulcus
What divides the temporal and parietal lobes?
The lateral fissure
What is an identifying feature of the occipital lobe?
The gyri are smaller and more tightly packed
What is the area ventral to the central sulcus called and what is its function?
The precentral gyrus. It is also called the Primary motor cortex, responsible for generating impulses for motor neurons.
What is the area ventral to the precentral gyrus called?
It’s the ‘planning area’, responsible for conscious planning of movements
What is the area posterior to the central sulcus called and what is its function?
The postcentral gyrus- also called the primary somatosensory cortex. It’s responsible for integrating all sensory information from the body as well as proprio sensation- knowing where your body is.
What is a motor/sensory homunculus?
A kind of map illustrating where in the brain the nerves/neurons for each area are located. The size of their representation is determined by the number of nerves/neurons for that particular part, rather than size alone.
Where is brocas area and what does it do?
It is ventral to the precentral gyrus in the planning area of the frontal lobe, between the middle and inferior gyri. It is responsible for forming speech. It is positioned near the homuncular mouth area of the precentral gyrus
Where is Exener’s and the eye area and what do they do?
Exener’s= hand area. Both are located in the planning area ventral to the precentral gyrus. They are responsible for fine motor movements of the hand and eye. This makes them important for reading and writing
Where is the primary auditory cortex and what does it do?
It is in the superior temporal gyrus, and maps sounds we hear in a tonotopic fashion- ie it separates high from low noises. It doesn’t interpret the sound, sending it to Wernicke’s area for this
What and where is Wernicke’s area?
It is also in the superior temporal gyrus, surrounding and just posterior to the primary auditory cortex. It makes sense of the tones the primary auditory cortex sends to it, making it a secondary auditory cortex.
What are the supramarginal gyrus and the angular gyrus and where are they?
They are in the inferior parietal lobule, with SM ventral to A. SM is responsible for reading interpretation/planning while A is responsible for writing planning and interpretation.
There is a white matter bridge between these areas and the areas of the eye and hand in the planning area, allowing them to talk to the motor nerves which initiate reading and writing.
What is the arcuate fasciculus and what does it do?
It connects Wernicke’s area and broca’s area, allowing you to know what you want to say (from W) and to be able to mechanically say it (from B)
What and where is the primary visual cortex?
It is located at the occipital pole, the most posterior part of the brain. It extends within the brain, separated by the calcarine sulcus, with granule cells which allow the rudimentary visual information to come through. It then sends this to the supplementary visual cortex.
What and where is the supplementary visual area?
It is posterior to the parieto-occipital sulcus and runs all the way down the back of the brain. It interprets sight.
What are the 5 groups of vertebrae/nerves in the spinal cord and how many of each?
Cervical- 8 Thoracic- 12 Lumbar- 5 Sarcal- 5 Coccygeal- 1
Where does the spinal cord itself end?
Between L1-2
What is the basic setup of the spinal cord?
Two roots coming in either side: Dorsal (with a ganglion) and ventral.
Circular, with an anterior median fissure on the front and a posterior median sulcus on the back
Gray matter is ‘butterfly shaped’, and separated into 3 horns: anterior, posterior and lateral
Central canal is located in the middle of the gray commisure
The white on either side of the gray commisure are called the anterior and posterior white commisure.
Posteriorly, there are 2 pairs of white columns.
The outer pairs are the cuneate fasciculii (Present C1-T8)
The inner pairs are the gracile fasciculii
There are also two anterior spinothalamic tracts and two lateral corticospinal tracts
What is a dermatome?
An area of skin supplied by a single spinal nerve
What are the different types of receptors?
Encapsulated or free nerve ending receptors
What are the types of encapsulated nerve endings and what do they do?
Meissner corpuscles: detect touch sensation
Pacinian corpuscles: detect pressure sensation
What do the free nerve endings detect?
Pain and temperature sensations
Which nerves out of encapsulated or free are myelinated?
The encapsulated ones are myelinated. They conduct their signals at approx. 50m/s-1 while free endings conduct at approx. 1m/s-1
What is discriminative vs non-discriminative sensation?
- Discriminative means you can accurately determine where two different points of contact are- eg. touch and pressure
- Non- discriminative means you can’t- you know a sensation is in an area, rather than a specific location. Eg. temperature.
How does information about touch/pressure reach the spinal cord?
Stimulus applied to skin –> Encapsulated nerve ending receives it –> Forms a generator potential –> Conducted along myelinated axon –> Posterior root –> Cell body in posterior root ganglion –> (Posterior column) posterior gray horn (depending on whether it’s a spinal reflex)
How does information about temperature/pain reach the spinal cord?
Stimulus –> free nerve ending receives it –> generator potential formed –> conducted along unmyelinated axon –> Posterior root –> Posterior root ganglion –> posterior gray horn
What is the pathway of discriminative sensation through the spinal path?
Called the Dorsal-Column- Medial Lemniscus pathway.
- 1st order nerve enters through dorsal root into the gracile or cuneate fasciculus
- Ascends fasciculus until it reaches the gracile or cuneate nuclei in the medulla
- Synapse with 2nd order nerve
- Decussates via the internal arcuate fibres
- Ascends out of the dorsal columns up through the medial lemniscus
- Enters the ventral-posterior nucleus of the thalamus
- Synapses with 3rd order nerve
- Crosses the internal capsule to the primary somatosensory cortex
What are the 3 different types of nerves in the sensory tracts?
1st order, 2nd order and 3rd order
What are 1st order nerves?
Convey impulses from the skin to the 2nd order nerves
What are 2nd order nerves?
Convey impulses from 1st order nerves to 3rd order nerves
What are 3rd order nerves?
Convey impulses from 2nd order nerves to primary somatosensory cortex
What is the pathway for non-discriminative sensation to the cerebral cortex?
Called the lateral spinothalamic tract
- 1st order nerve enters through the dorsal root, into the dorsolateral tract of lissauer
- Synapses with a 2nd order nerve
- Decussates via the anterior white commissure
- Enters the lateral spinothalamic tract
- Ascends through the medulla where it joins the medial lemniscus pathway in the pons
- Reaches the ventral-posterior nucleus of the thalamus
- Synapses with a 3rd order neuron
- Goes through the internal capsule to the somatosensory cortex
What is associative sensory loss?
Loss of discriminative and non-discriminative sensation in the same side of the body due to a lesion occurring after both types of pathway have decussated. (occurs in the opposite side to lesion)
What is dissociative sensory loss?
Loss of discriminative sensation in the same side of the body as the lesion but loss of non-discriminative sensation in the opposite side of the body. This is due to a lesion occurring when the discriminative pathway has not decussated, but the non-discriminative has.
What is an upper motor neuron?
A motor neuron controlled by the basal ganglia which runs from the primary motor cortex down to the spinal cord.
What is a lower motor neuron?
A motor neuron regulated by the upper motor neurons which runs from the spinal cord to the muscles to cause them to contract.
What are the basal ganglia?
5 Gray matter nuclei which help to control and coordinate movement
What is the motor pathway taken to control movement?
Called the corticospinal tract (pyramidal tract)
- UMNs start out in the primary motor cortex.
- Run down the internal capsule, down through the pyramidal tract in the pons and down to the medulla
- 85% decussate here, and from both sides this looks like a pyramid hatching shape
- Run down the lateral corticospinal tract
- end in the lateral white matter, synapse with a LMN
- LMN exits the spinal cord via anterior root
- 15 % do not decussate in the medulla
- Run down the ventral corticospinal tract
- Decussate at the individual spinal level
- Synapses with (interneuron) LMN
- LMN exits the spinal cord via the anterior root
What are the 5 basal ganglia and their relative positions?
Caudate Nucleius: Most superior and anterior
Putamen: Most lateral and inferior to caudate nucleius
Globus Pallidus: medial to the putamen. External is lateral to internal segment
Sub- thalamic nucleus: Inferior to thalamus. Medial
Sibstantia Nigra: Pars compacta and reticulata. Inferior to sub thalamic nucleus.
What is the connective pathway between the cerebral cortex and the striatum? (Inc. neurotransmitters involved)
Neuron from cerebral cortex planning area talks to the striatum to clarify what movements are needed. Uses GLUT
Neurons between striatum to GP ex and GP int.
Neuron from GP int. to VA-VL area of thalamus. Uses GABA. This is inhibitory and suppresses successive nerves from firing. If suppressed, it allows nerves to fire uninhibited- a balance is required.
Neuron from VA-VL to cerebral cortex, where is uses GLUT to activate an UMN
What are the functions of the basal ganglia?
- Mood expression through movement- ability to display our mood
- Initiation of movement
- Fine motor control
What is the pathway between the cerebellum and the UMNs?
Neuron from Cerebellum to VA-VL using glutamate to stimulate the following neuron
Neuron from VA-VL to the UMN of the cerebral cortex
What are the functions of the cerebellum?
- Coordination of movement
- Unconscious movements
- Balance
- Ballistic movement
- Termination of movement
What is interesting about ballistic movements?
At first, they are regulated by the cerebellum. However, as we practice, these fast unplanned movements become planned, so control is gradually shifted to the basal ganglia.
What is tremor?
Alternating contraction and relaxation of skeletal muscles, causing a shake
What is bradykinesia?
Slowness of initiation of movement
What is hypokinesia?
Decreased range or ability to move
What is the function of substansia nigra?
Make and send dopamine to the forebrain
What does dopamine do in the forebrain?
Smoothes movement and controls mindstate
How does dopamine reach the striatum?
It is released as a neurotransmitter from a lightly myelinated neuron
What is the pathway between the Substansia nigra and the striatum?
A neuron runs between the pars compacta and the striatum, using dopamine as a neurotransmitter
This pathway innervates the cells in the putamen which stretch to the GP. It holds them in a ready to fire position.
What about the striatum means that it is very sensitive to GLUT?
It is tonically active- the presence of dopamine ensures that it is always on the brink of releasing an AP, so can be easily tipped over the edge by GLUT.
What is the underlying cause of parkinson’s disease?
The SN pars compacta stops producing dopamine. This may be due to O2 depletion as this area is very sensitive to the concentration of oxygen
What does the inability of the SN PC to produce dopamine mean for the rest of the pathway?
The striatum is not held at an almost-firing position by the dopamine, so when GLUT arrives no AP is generated
As a result, there is no conduction from Putamen to GPe and none from GPe to GPi. Consequently, the inhibitory pathway from GPi to the thalamus is allowed to fire unchecked, and inhibits movement as the UMN is no longer able to be activated.
Hypokinesia (reduction in cortical excitation) results.
What do the two halves of the putamen do?
Upper: Movement
Lower: connected to the frontal lobe and limbic system. (mood)
What does low/high dopamine mean psychologically?
Low: Poor movement, catatonia
High: Wild movements and in extreme cases, psychosis
What are the current treatments for parkinsons disease?
- Dopamine replacement drugs (L-Dopa)
- Pallidotomy of GPi
- Thalamotomy of VA-VL
- Deep brain stimulation
Why and how does L-Dopa work?
It replaces the dopamine the SN is no longer producing. Simple dopamine was used originally, but could not be digested or cross the blood/brain barrier.
However, it causes extreme swings- in mood as well as movement ability. Also, it only works for 8 years after the commencement of treatment
What is a pallidotomy and why does it work?
A lesion is created in the internal GP. This kills GABA cells, preventing over-inhibition of the UMNs.
However, the GP is very close to other crucial structures such as the internal capsule, so it is very risky
What is a thalamotomy and how does it work?
A lesion is created in the VA-VL GABA receptors of the thalamus. This means the inhibition cannot be received as well. It has the same effect as a pallidotomy but there is less change of hitting other important structures
What is DBS?
Deep brain stimulation involves connecting electrodes to the GPi or sub-thalamic nucleii in order to turn the inhibitory neurons on or off as needed. It is preferable to the other surgeries as it is reversible, and can be adjusted to different degrees.
However, it is expensive and has the most benefits for the most serious patients, so less serious cases may not benefit so much.
What is the effect of a lesion in broca’s area?
Nonfluent aphasia- you know what you want to say but can’t say it
What is the effect of a lesion in wernicke’s area?
Fluent aphasia- you can form words but they have lost their meaning
What is the effect of a lesion in the precentral gyrus?
Loss of ability to move the corresponding body part on the opposite side
What is the effect of a lesion in the postcentral gyrus
Loss of sensation on the corresponding body part on the opposite side
What is the effect of a lesion in the primary auditory cortex?
Loss of ability to hear in opposite ear
What is the effect of a lesion in the right hemisphere?
Loss of nonverbal expression, spatial awareness, abstract thinking, artistic and musical skills, emotional expression and ability to recognize objects
What is the effect of a lesion in SMAGLA?
Issues reading
What is the effect of a lesion in AGLA?
Issues writing
What is the effect of a lesion in the arcuate fasciculus?
Understand language (eg. can read), but cannot say what they mean, even though they can physically make sounds
What is the effect of a lesion in the brainstem?
Associative sensory loss: discriminatory and non-discriminatory sensation both lost on the corresponding part of the body on the opposite side to the lesion
What is the effect of a lesion in the spinal cord?
Dissociative sensory loss: discriminatory sensation lost on the same side of the corresponding body part as the lesion, while non-discriminatory sensation is lost on the opposite side to the lesion in the corresponding body part
What is the effect of a lesion in an UMN?
Spastic paralysis- increase in corresponding muscles’ tone and tension as control over LMNs is lost and they are not prevented from firing. Depending on where the lesion and the decussation for a UMN is, it may be the same or opposite side of the body
What is the effect of a lesion in a LMN?
Inability to move the body’s innervated part on the same side as the lesion (flaccid paralysis)
What is the effect of a lesion in the cerebellum?
Overshooting of movement, loss of balance and coordination, poor ballistic and unconscious movement on the same side of the body as the lesion
What is the effect of a lesion in the basal ganglia?
Difficulty initiating movement- brady/hypokinesia.
Impairment of fine motor movements, inability to display mood through movement all on the opposite side of the body as the lesion. Poor mood, catatonic or psychotic state.
