GEP (Life Control) Week 1 Flashcards
What are the devision of the brain
Forebrain
Cerebrum (outer):
Frontal lobe
Parietal lobe
Temporal lobe
Occipital lobe
Diencephalon (inner)
Thalamus
Hypothalamus
Midbrain
Tectum (roof/quadrigeminal plate)
Cerebral peduncles:
Crus cerebri
Tegmentum
Substantia nigra
Hindbrain
Brain stem:
Pons
Medulla Oblongata
Cerebellum
What is the cerebrum, what does it do and what does it consist of
Conscious thought processes and intellectual function
Memory storage, processing and retrieval
Conscious and subconscious regulation of skeletal muscle contraction
Frontal (motor activity, higher functioning)
Parietal (sensory areas [cortex])
Temporal (hearing)
Occipital (vision)
What are the motor and sensory regions of the cerebral cortex
What is the diencephalon
The diencephalon is beneath the cerebrum, and is the deep area of grey matter. Its main structures are the thalamus, which is the relay and processing centre, and the hypothalamus, which is involved in hormone production and emotional control.
What is the brainstem
Midbrain, Pons & Medulla Oblongata
Relay centre between brain and spinal cord
Reflex centres for autonomous control
What is the cerebellum and what does it consist of
Functions:
Coordination of complex somatic motor patterns
Balance
Refined movements
Describe the different regions of the skull
What are the different layers of the meninges and how CSF is made
What are the 12 cranial nerve
Oh Oh Oh To Touch And Feel Very Good Velvet Ah Heaven
What are axons, action potential and neurotransmitter
To discus neurotransmitters, we must quickly discuss how stimuli and responses travel through the nervous system. The brain, amongst other things is made up of neurons. These these have a main cell body which houses its nucleus, but then have losing finger like projections called axons. It is down these axons at action potentials are sent in response to a signal. Action potentials are when there is increase in voltage to the point of which a threshold potential is reached, this causes an influx of ions that causes depolarisation of the cell. This depolarisation spreads down the axon to the axon terminal. At this point, the axon terminal is connected to other neurons via synapses. These synapses allow to passage of impulse through neurons to desired areas. It is at these synapses that neurotransmitters play a pivotal role. As an action potential reaches the terminal, it depolarises the presynaptic membrane, which opens up calcium channels, causing an influx of calcium ions. This triggers the exocytosis of neurotransmitters from vesicles residing in the axon terminal into the synaptic cleft. These neurotransmitters then attach to receptors on the post synaptic membrane (another neuron), causing them to open and allow an influx of ions that fires off an action potential in the new neuron. Different neurotransmitters have different functions, some excitatory, some inhibitory.
What are the different types of neurotransmitter
What is the gross anatomy of the eye
Starting off with structure the eyes, it is highly sophisticated catcher of light. Through its structure is able to take in light, optimise its ability to excite receptors within the eye to provide a better image to process, before sending it down drive to be processed in the occipital lobe. The first main thing to state is that it is obviously spherical, allowing for it catch as much light as possible. It is made up of 3 layers.
The outer fibrous layer consists of the sclera and cornea, which are continuous with each other, the sclera is white, and the cornea (the anterior part of the eye) is transparent, allowing for light to enter the eye. The main function of this layer is to provide shape to the eye and support the deeper structures.
The next layer is the vascular layer, consisting of choroid vessels; that supplies the outer retina with nutrients; and the ciliary body. The body consists of muscle (meridonal fibres and circular fibres) and process, which allows a connection point to suspensory ligaments called zonules. The ciliary body has many important roles, mostly producing aqueous fluid humor. This is a fluid that (along with vitreous fluid) fills the eye, providing its structure. The fluid provides enough pressure to maintain the structure, and is accomplished through a delicate interplay between input and output of fluid that will be discussed later. A third component of this layer is the iris, which is found between the lens and the cornea, and what changes shape to control the entrance of light.
The final and most inner layer of the eye is the retina, which has the role of detecting light ad send the stimulus into the brain for processing. It is composed of two main layers, the pigmented outer layer (retinal pigment epithelium) which connects to the choroid layer, and a neural layer, which consists of photoreceptors called rods and cones, which are stimulated by light and send impulse down neurons. These neurons meet up at the optic disc, which creates the beginning of the optic nerve. On the centre of the posterior wall of the retina is a structure called the macula. It is a highly pigmented area, containing a depression called the fovea centralis, which contains a high concentration of cone photoreceptors, giving an area of high visual acuity. This is the area we use when reading for example.
What are the choroid and retina
The next layer is the vascular layer, consisting of choroid vessels; that supplies the outer retina with nutrients; and the ciliary body. The body consists of muscle (meridonal fibres and circular fibres) and process, which allows a connection point to suspensory ligaments called zonules. The ciliary body has many important roles, mostly producing aqueous fluid humor. This is a fluid that (along with vitreous fluid) fills the eye, providing its structure. The fluid provides enough pressure to maintain the structure, and is accomplished through a delicate interplay between input and output of fluid that will be discussed later. A third component of this layer is the iris, which is found between the lens and the cornea, and what changes shape to control the entrance of light.
The final and most inner layer of the eye is the retina, which has the role of detecting light ad send the stimulus into the brain for processing. It is composed of two main layers, the pigmented outer layer (retinal pigment epithelium) which connects to the choroid layer, and a neural layer, which consists of photoreceptors called rods and cones, which are stimulated by light and send impulse down neurons. These neurons meet up at the optic disc, which creates the beginning of the optic nerve. On the centre of the posterior wall of the retina is a structure called the macula. It is a highly pigmented area, containing a depression called the fovea centralis, which contains a high concentration of cone photoreceptors, giving an area of high visual acuity. This is the area we use when reading for example.
What are the muscles of the eyes and eyelid
Supporting structures of the eye include the eyelids and extraocular muscles. The eyelids obviously cover the eyes, providing protection to the eyes, as well as helping keep them lubricated (when we blink etc). It consists of 5 main layers (superficial to deep):
Skin and subcutaneous tissue
Orbicularis oculi (muscle that closes the eyelid, innervated by facial nerve)
Tarsal plates (glands to secrete oil into eye to prevent evaporation of tear film)
Levator apparatus (levator palpebrea superioris and superior tarsal muscle, opens eyelids, innervates buy occulomotor nerve)
Conjuctiva
*Sensory innervation: ophthalmic nerve (upper) and maxillary nerve (lower)
Innervation is important as something to look out for on examination is ptosis, which is caused then there is palsy of CNIII, causing the drooping eyelid.
What are the extraocular muscles of the eyes
The extraocular muscles allow for the movement of the eyes. They consist of six different muscles (for each eye), all allowing for a different movement of the eye: (see table)
SO4 LR6, rest are CNIII. Sometimes they are hard to comprehend, but the best way to remember them is to know that four rectus muscles, and these correspond to either up, down, left or right (in essence). The obliques are a little more complicated, but the best way to understand is to look at them using a YouTube video. See how if you pulled them, what movements they would make, and through that is becomes more manageable. But put simply, the obliques do the opposite of their name. Superior oblique helps the eye move down and out, the inferior helps the eye move up and out.
These are the main structures of the eye that should help us understand the processes that allow for converting light into visual images.
What are the directions and movements of the extraocular muscles
Describe the visual pathway
- Light hits cornea (tear film)
- Light is refracted (air->fluid medium)
- Fine focusing from lens
- Light hits retina
- Phototransdution
A light ray hits the eye at the cornea, which begins the process bending the light towards the retina through refraction. Refraction is phenomenon in which when light enters a different medium (i.e from gas to liquid) its trajectory is redirected. That is the level in which you need to understand refraction, as we just need to appreciate that as light hits the cornea, it is redirected towards the retina and more specifically towards the photoreceptors. To be even more specific, it is not the cornea itself that refracts light. A tear film (a lipid bilayer) in front of the cornea allows refraction to happen. The majority of the refraction required for light to hit the retina is done at this point. It then can pass through aqueous fluid within the anterior chamber and hits the lens. The lens then makes fine final adjustments to ensure the light hits the retina. It is here that Phototransduction occurs.
Phototransduction is the process in which light is converted to a sensory impulse, that is subsequently sent into the brain to be processed. This process involves several different cells.
What are the 2 type of photoreceptors and thier role
Two main types, rods and cones
Cones split into three other types, based on wavelength range they capture
Rods are scotopic, useful in dim light
Cones are phototopic, good for colour vision, visual acuity and edge detection
What is the process of phototransduction
When a light ray moves into a photoreceptor, it hits an opsin molecule, which converts the pigment from its cis form to a trans form, separating it from the opsin molecule. This opsin is the ‘activated’ and free to roam the cell. This free form of opsin is then able to activate a protein called transducin, which in turn is able to activate an enzyme called phosphodiesterase (PDE).
Usually in photoreceptors, when no light has been detected, gaunylate cyclase is able to convert GTP to cyclic GMP, which binds to channels on the photoreceptor membrane and allow ions into the cells, creating receptor potentials (similar to action potentials), which travels down the photoreceptor cell and releases the neurotransmitter glutamate. This causes an inhibitory post synaptic potential, preventing the release of neurotransmitters at the bipolar cell-ganglion cell synapse. With no neurotransmitter release, they do not send an impulse to ganglion cells, and no stimulus is sent down the optic nerve and to the brain.
When light is detected and PDE is produced, it breaks down cGMP (deactivating it), preventing it from binding to ion channels, which as a result close. No movement of ions into the photoreceptor repolarises the cell into a hyperpolarised state. This stops neurotransmitter release into the synaptic cleft between photoreceptor and bipolar cell. Little presence of glutamate stimulates the bipolar cell, keeping ions in the bipolar cell and depolarising the cell, allowing for potential to be sent through the cell. This causes the release of glutamate at the bipolar cell-ganglion cell synapse, causing an excitatory post synaptic potential. This action potential spreads down the ganglion axon, and conjoins with other axons towards the optic disc, forming the optic nerve.
This is the main process, but horizontal and Amacrine cells can be found at the different synaptic junctions (PR-BC, BC-GC respectively). Their role is to release various neurotransmitters that can inhibit and the surrounding cells. This prevents hypersensitivity to light, allowing for the stimulus to be very precise, increasing acuity.
Desribe the visual pathway
Signal sent down optic nerve. Nasal tracts decussate at the optic chiasm
Image is flipped (L->R) and inverted to create final image we perceive
At this point the optic nerve has been stimulated, and it sends the impulse down the optic nerve pathway in order for the image to be processed. The optic nerve leaves through the optic cavity and passes through the optic canal. It passes through the superior orbital fissure and converges with its contralateral counterpart at the optic chiasm (located superior to the sella turcica of the sphenoid bone). Here nerves fibres form the nasal aspect of the retina decussate and run along the contralateral side, this is so all images detected by the left side of the eyes (images from the right side) are processed in the left side of the brain. They travel down the optic tract to the Lateral Geniculate Nucleus (LGN), a second order sensory neuron in the thalamus. The LGN then sends to impulse along axons called optic radiations with loop through either the parietal or temporal lobs directly to the calcarine sulcus of the occipital lobe, where the image is processed. The route of the radiation corresponds with visual field, with parietal radiations corresponding with lower visual fields (and vice versa). The image from both eyes is merged to form a final image. Here, the body then inverts and flips it left to right to give us information that is correctly orientated within space. This is how our eyes and brain are light and convert it to an image.
We now have our image, which we the can create a response to. In terms of how the eyes can react, there are a number of things our eyes may do, mostly to create a better image for us to interpret.
Describe the pupillary light Reflex
- Pupils constriction/dilate in response to variable light levels
- Constriction is a parasympathetic response
- Stimulus sent to occipital lobe, which causes a bilateral efferent response via the Edinger-Westphal nucleus.
- Constriction of sphincter pupillae muscle->contriction of pupil
- Dilation is a sympathetic response
- Stimulus she to ciliospinal centre. Postsynaptic neurons pass down to cervical chain, then up carotid plexus to ophthalmic nerve
- Constriction of dilator pupillae muscle-> dilation of pupil
The first response from the body is to dilate or constrict the pupil. This is done depending on distance and light. If the object is too far away or too dark, the pupil can dilate to allow more light in. If too close or too bright, the pupil can constrict. This response is a balance between sympathetic and parasympathetic response. Parasympathetic innervation leads to pupillary constriction. A stimulus is sent to the occipital lobe, which then sends a bilateral response through the Edinger-Westphal nucleus near the occulomotor nerve nucleus. The efferent response then travels along the third cranial nerve and synapses at the cilliary ganglion, causing the sphincter pupillae muscle to contract, constricting the pupil.
Sympathetic innervation leads to pupillary dilation. Once the afferent impulse reaches to cortex it stimulates the ciliospinal centre. Post synaptic neurons take a convoluted path down the brain stem and exit at the cervical sympathetic chain and the superior cervical ganglion. They synapse at this ganglion, where third-order neurons travel through the carotid plexus and enter the orbit through the first division of the trigeminal nerve (Ophthalmic nerve). This stimulates constriction of the dilator pupillae muscle, dilating the eye.
It is important to note that whilst the stimulus may be unilateral, when forming an efferent response, the nuclei send bilateral signals, so that both eyes respond to the stimulus.
How does accommodation
- Fine focus done by lens
- Focuses light onto macular region (of concerted photoreceptors)
- High level of acuity
- Lens is thickened or narrowed to refract light so that it focuses onto this retina.
- In accommodation, ciliary body contracts, loosening zonules, thickening the lens, bending light to greater degree
- Stimulated by occulomotor nerve (CNIII)
Another response would be if the image was not focused. Whilst the majority of light is focused onto the retina via the cornea, fine focus is controlled by the lens. This is all to do with ensuring the light hits the macular area, where this a high concentration of photoreceptors which would increase acuity. If the image is blurred, this may be because the light ray is focused in front of or behind the retinal wall. In response to this, the lens can be made thicker or thinner in order to aim light onto retina. This done through use of the ciliary body and zonules. The zonules are suspensory ligaments, and when the ciliary muscle is at rest, the zonules are held taught, keeping the lens thinner and more concave. If an object is too close, then an impulse stimulates the cilliary ganglion (form CNIII) causing contraction of the ciliary muscle. This pulls on other ligaments that move the lens anteriorly, loosening the zonule and allowing the lens to thicken and become more convex.
What is convergence
A final response to an object being too close or not in focus would be to move the eyes. This is so that the eye can target photoreceptors closer to the macula of the eye, which has a higher concentration of photoreceptors and allows for greater acuity. The response from the extraocular muscles would be to make the eyes converge, that is make them come together. To do this, the medial rectus muscles would be stimulates via the occulomotor nerve, as well as the superior oblique which rotates the eyes inferiorly and medially. This would be done via stimulation of the abducens nerves (CNIV).
Define Misosis, Accommodation, Convergence
Misosis (pupil constriction-pinhole effect for focusing)
Accommodation (brings closer image into focus)
Convergence (eyes come together to centre image)
