PSY3010S- Functional Neuroanatomy Notes PDF

Preview

Summary

FUNCTIONAL NEUROANATOMYOrganisation of the Nervous System: - Nervous system is divided based on different neuronal properties and functions - Our NS is divided into two parts:  Central Nervous System (CNS) o Brain + Spinal Cord o Neuropsychologists are concerned with the functioning of the brain an...

Description

FUNCTIONAL NEUROANATOMY Organisation of the Nervous System: - Nervous system is divided based on different neuronal properties and functions - Our NS is divided into two parts:  Central Nervous System (CNS) o Brain + Spinal Cord o Neuropsychologists are concerned with the functioning of the brain and the spinal cord, and how damage to these systems may reflect in our behaviour, cognitions, and emotions.  Peripheral Nervous System (PNS) o Anything periphery (outside) of the CNS – the Nervous System aside from the CNS. o Somatic Nervous System: deals with voluntary behaviour o Autonomic Nervous System: deals with involuntary behaviour + further divided into Sympathetic Nervous System & Parasympathetic Nervous System.

-

-

Central Nervous System and Peripheral Nervous System constantly communicate They exchange sensory and motor information via:  Spinal nerves: contained in spinal cord  Cranial nerves: bypass spinal cord, carry info directly to brain Sensory information is that information concerning the senses (e.g., about taste or sight) and motor information is that information concerning movement (e.g., how to move your hand to perform a task). The spinal nerves are housed/contained within the spinal cord (this is where we find them) and the cranial nerves carry information directly to the brain – they bypass the spinal cord.

Peripheral Nervous System: Somatic Nervous System: - Interacts with external environment

- Afferent nerves: carry messages from sensory organs to CNS - Efferent nerves: carry motor signals from CNS to muscles (perform action/motion) Autonomic Nervous System: - Helps regulate body’s internal environment - Controls internal organs - Sympathetic division  Involved in activities that expend energy  Prepares body for action - Parasympathetic division  Acts to conserve energy

Central Nervous System: - Has important evolutionary significance since it is what allows us to adapt to our environment. - That is why it is heavily protected:  Bony encasing of the skull  Spinal column surrounding the spinal cord  Meninges - CNS is the most well-nourished part of the body Important Terminology: Planes Bisecting The Brain: - Coronal:  Sliced ear to ear to separate front from back  aka. Frontal - Horizontal:  Sliced so that the top of the brain is separated from the bottom  aka. Axial - Sagittal:  Sliced so that the left side is separated from the right side

- One can get different info depending on what viewpoint you are taking—very helpful Directions of Orientation: - Anterior:  Toward the front/front end - Posterior:  Toward the back/back end - Inferior:

 Toward the bottom of the body/below - Superior:  Toward the top of the head/body/ above - Medial:  Toward the middle/midline - Lateral:  Away from the middle/midline— toward the side - Rostral:  Toward the nose - Caudal:  Toward the tail/rear - Proximal:  Near the trunk/centre - Distal:  Away from the centre - Dorsal:  Toward the back - Ventral:  Toward the belly/front Laterality: - Terms we use to describe which side of the brain or body - Ipsilateral:  On the same side  His left arm and left leg are both paralysed – he has ipsilateral paralysis of arm and leg. - Contralateral:  On the opposite side  His left arm and right leg are paralysed – he has contralateral paralysis of arm and leg. - Bilateral:  On both sides  Her arms are both paralysed – she has bilateral paralysis of her arms. - Unilateral:  One side of the body  Only her left leg is paralysed – she has unilateral paralysis of her leg. - Particularly important to understand because in terms of brain structure and function, to a large extent damage on the left side of the brain will result in the contralateral side of the body being affected and damage on the right side of the brain will therefore be associated with left side of the body being affected. - However, damage to certain structures can result in ipsilateral effects.

-

-

-

If the right arm is paralysed and the left leg isn’t, it is highly unlikely that only one side of the brain is affected, and is also much more likely that there may be some form of faking it, when it comes to brain injury Distinguish whether someone is faking their symptoms, and whether they are doing so consciously (malingering) or unconsciously (a conversion disorder). In essence, the side of the body that is affected can tell us something about which side of the brain may be involved.

Spinal Cord: Structure: - Spinal Cord= long tube-like structure that begins at the end of the brainstem (just inferior/below the brain) and continues until almost the bottom of the spine. - The spinal cord and brain are so important, so it is essential that our body has mechanisms in place to protect them - From below the brainstem until almost bottom of spine - Sensory info enters dorsally and motor info exits ventrally - Mechanical protection of spinal cord:  Spinal column o The bony encasing of the vertebrae. o Composed of 33 individual vertebrae (i.e., back bones). o These vertebrae protect the spinal cord, and are separated by disks made of cartilage, which acts as cushions so that every time we move the forces, we generate are reduced by them.  Cerebrospinal fluid (CSF) o CSF is a fluid that runs through the entire CNS and allows for some cushioning as well.  Meninges o Three layers of tissue that cover the spinal cord. o They protect the entire CNS, not just the spinal cord. - Structurally, at every level of the spinal cord (i.e., every vertebra) we see what is called innervation of sensory and motor neurons - Innervation of 30 sensory and motor neurons  At every level there are a pair of afferent dorsal and efferent ventral root fibres entering and exiting to communicate with the brain and muscles  Nerves carry incoming sensory info and outgoing motor info  Here you can see a cross-section of one of the vertebrae in the spinal column. The blue afferent dorsal root fibres (one on each side) carries sensory





information into the spinal cord from the brain, and the red efferent ventral root fibres carry motor information away from the spinal cord to the muscles. This inflow of sensory info and outflow of motor instructions/info should make sense as the spinal cord is essentially given the sensory information to be able to “instruct’ the body what to do about it ‘motorily’. Essentially nerves carry incoming sensory info and outgoing motor info into and out of the spinal cord.

Components of a Spinal Nerve: - Sensory info entering the spinal cord dorsally (blue line) and then information is sent to the skeletal muscles and the bodily organs ventrally (red line)

Function: - The spinal cord is the highway for communication between the body and the brain - Relaying sensory and motor information to & from brain

-

Integration of information involving basic reflexive behaviour  Complex behaviour is not a spinal cord function - E.g.) when you touch a hot plate on the stove accidentally, the sensory information from the receptors in your hand are sent to the spinal cord and enter dorsally. For the most part, information then travels up the spinal cord to the brain (which is essentially an extension of the spinal cord) and is processed there at which point instructions are sent from the brain to the organs and muscles to do something about this sensory info. However, in this instance, our behaviour is reflexive. When we touch the hot plate of the stove, the sensory information from the receptors in your hand reach the spinal cord where they are immediately processed, and motor information is sent to your muscles to move your hand away. This happens very quickly, and for good reason – it has adaptive advantages (in other words, survival benefits). - So, while the spinal cord generally relays information between body and brain, it can bypass the brain in instances where reflexive behaviours are involved and immediate action is necessary. Pathology - When the spinal cord is injured, the exchange of information between the brain and other parts of the body is disrupted - Damage may result in sensory and motor impairments - Often permanent changes in strength, sensations, and other body functions below the site of injury - Usually, it is functioning below the injury site that is affected. The extent of the injury in terms of the ability to control your limbs after injury depends on two factors: (1) the site of injury and (2) the severity of injury. - Severity= the completeness of injury - Paralysis from a spinal injury= tetraplegia/paraplegia - Location/site and severity of injury determine extent of loss of functioning  Complete: o If all feeling (sensation) and all ability to control movement (motor function) are lost below the site of spinal cord injury  Incomplete: o If you have some motor/sensory function below the affected area, your injury is called incomplete o Varying degrees on incomplete injury  Tetraplegia: o Also known as quadriplegia, this means that yours arms, hands, trunk, legs and pelvic organs are all affected by your injury  Paraplegia: o This paralysis affects all/ part of the trunk, legs and pelvic organs Protection & Sustenance of the Brain: The Skull: - aka. The Cranium - Structure:

Cranial plates o Not fused yet at birth, but connected by membrane o Plates fuse around age 2 years o Fontanelles = soft openings where plates meet o The reason why these plates are not fused at birth is because at birth the brain is only 25% of its adult size, and reaches about 75% within the first year of life—much expansion and therefore a necessity for cranial plates to move a bit. o When the brain is injured, one of the complications/symptoms is that it swells – this is called Oedema. The brain and skull are essentially in what is called a zero-sum game once the plates are fused. If the brain swells, it has only the fixed space of the skull in which it can expand. If we cannot get the swelling down, the swelling will result in damage and/or death of brain cells as it hits the hard encasing of the skull.  Fossae o Ridges in base of skull which hold the brain in place  Foramina o Orifices (holes) allowing nerves and blood vessels to enter the brain via the base of the skull o Foramen magnum – largest, opening in occipital bone for spinal cord to pass through to the brainstem Function:  Skull encases the brain= protection  Liability to this ridged encasement—it limits space within which the brain can move—can cause damage to the brain if the brain needs more space (swelling during injury)  Sometimes because of increased intercranial pressure we see that the brain is displaced – it results in a herniation. In essence, the brain moves in whatever direction there is some ‘give’—very dangerous when parts of the brain end up in spaces that they should not be. o One such herniation is referred to as a transtentorial herniation= when the brain moves downwards in the skull because of increased pressure perhaps by a bleed in the brain. o The brain is then essentially pushed onto the base of the skull with all its many ridges and edges 

-

In this image on the right there is a bleed on the right and it’s placing pressure on the brain pushing it to the left of the image. You can see points 1; 2 and 3 are moving to the left and those dark blobs in the middle are the ventricles. You can see how they are also changing shape because of the pressure and are no longer symmetrical. Image is showing is two things: 1.) a midline shift, which is when the structures that are meant to be in one of the brain hemispheres move the other because of raised ICP. 2.) a herniation downwards (a transtentorial herniation) Points 3 and 4 show you how the structures are receiving some pressure downwards. Herniations and a midline shift are serious red flags and call for immediate ICP reduction.

Blood pooling

to

The Meninges: - Structure:  A set of 3 semi-permeable membranes that hold the NS in place.  Layered in a specific sequence, with spaces between the layers: Inner to outer o The inner layer ‘against the brain’ = Pia Mater (meaning soft) & it’s the thinnest layer. o Next we have a space through which CSF flows= Subarachnoid Space: it’s below (sub) the arachnoid membrane & the second of the membranes of the meninges. o Arachnoid Membrane: means spider -- because of the web-like structure of the membrane o Tightly layered upon the arachnoid mater is the Dura Mater = the toughest of the membranes & consists of two layers= meningeal layer and the periosteal layer. o Between the dura and arachnoid membrane there is the Subdural Space= potential space-- say ‘potential’ since it can be filled with blood if there is a bleed in the brain. When we talk about bleeding in the brain we can therefore talk about subdural or subarachnoid bleeds.

-

-

Function:  Protective covering o The CSF in the subarachnoid space basically adds some cushioning if the brain is shaken a bit.  No function in cognitive activities Pathology:  Meningitis – infection of the meninges o Most common causes: bacteria, viruses o Other causes: fungi, cancer, chemical irritation, drug allergies o Some forms are contagious o Test via blood test o Signs: headache, stiff neck, sensitivity to light, nausea and vomiting.

The Ventricular System: - Structure:  Interconnected ventricles (2 x lateral, third, fourth)  Ventricles are essentially fluid-filled spaces – the fluid being CSF.  There are two lateral ventricles – one in each hemisphere of the brain (the two biggest ventricles)—connect with the third ventricle, which links to the cerebral aqueduct, and then the fourth ventricle.  Choroid plexus – cells produce CSF in the lateral ventricles  If brain tissue swells it can press against the ventricles, distorting the ventricles’ shape and size, and at the same time damaging the tissue pressing against the ventricles= Distortion by brain damage (zero-sum game) - Route of CSF:  New CSF circulates throughout this system every 6-7 hours  Produced in the Choroid plexus in lateral ventricles  The travels through foramen (opening) of Monro into 3rd ventricle  Then enters cerebral aqueduct (aqueduct of Sylvius) to 4th ventricle  Membranous roof of 4th ventricle has foramen of Magendie (posterior) and foramina of Luschka (anterior) (2 openings), allowing CSF to flow outside brain and recirculate  Cycle complete via continuous reabsorption of CSF from subarachnoid space - Function:  It acts as liquid buffer. The fluid-filled spaces act as cushions if forces are exerted on the brain.

It assists with waste disposal into the venous system which takes waste away from the brain.  The ventricular system influences cognition – it does so indirectly as its size has an indirect influence on cognition. If it is too big – if it takes up more space, leaving less space for the brain in the skull. Pathology  Alterations of intracranial pressure (ICP)  When the brain swells, it places increased pressure on the skull= intercranial pressure.  If ICP is too high= brain damage given the zero-sum situation.  If the ventricles are too large, it will increase ICP.  E.g.) Hydrocephalus o the ventricles become too large o Can happen for a number of reasons: could happen because of a blockage between the different ventricles leading to a build-up of CSF in one part of the system (also known as communicating hydrocephalus) OR because of abnormal production of CSF by the choroid plexus resulting in too much CSF in the ventricles (known as non-communicating hydrocephalus). o It is also something seen in older adults where it is associated with a number of symptoms which we will cover shortly = normal pressure hydrocephalus (NPH). 

-

Hydrocephalus

Normal

o Often severe cases in infants are obvious. o Since their cranial plates are not fused yet, the shape of the head can be grossly distorted. o If we look on a scan, you can see to the right how the lateral ventricles are hugely enlarged. o Often hydrocephalus seen in infants is a result of a blockage in the pathway of the CSF (e.g., an infiltrating tumour).

-

Normal Pressure Hydrocephalus:  Variant of hydrocephalus in adulthood o Initial increase in CSF pressure, then back to normal o Ventricles expand, but do not reduce after pressure returns to normal o Possible causes:  Subarachnoid haemorrhage  Head trauma  Meningitis o Triad of neuropsychological symptoms  Balance or gait problems  Urinary incontinence  Dementia The Vascular System: - Structure:  Veins o take blood away from the brain  Arteries o supply the brain with blood (so take it to the brain). o Right and Left Internal Carotid Arteries – supply anterior part of the brain o Each divides into Anterior Cerebral Artery (ACA) and Middle Cerebral Artery (MCA) – connected by the Anterior Communicating Artery o Two Vertebral Arteries – supply posterior part of the brain  Basilar Artery splits into left and right Posterior Cerebral Arteries  Cerebral Arteries:

Artery Name

Originates From

Distributes To

Right internal carotid

Branches of the aortic arch, which arises from the left ventricle of the heart Branches of the aortic arch, which arises from the left ventricle of the heart Branches of the aortic arch, which arises from the left ventricle of the heart Branches of the aortic arch, which arises from the left ventricle of the heart Joining of the two vertebral arteries at the level of the brainstem A division split off from the basilar artery A division split off from the basilar artery Divides off from the internal carotid artery on each side of the body Divides off from the internal carotid artery on each side of the body

Anterior portions of the brain

Left internal carotid

Vertebral artery #1

Vertebral artery #2

Basilar artery Right posterior cerebral artery Left posterior cerebral artery Anterior cerebral artery Middle cerebral artery

Anterior portions of the brain

Posterior portions of the brain

Posterior portions of the brain

(Mostly) Posterior regions (Mostly) Posterior regions (Mostly) Posterior regions Anterior paramedian cerebral hemisphere Lateral hemisphere; most of the basal ganglia



-

-

-

Circle of Willis o The vascular system in the brain is essentially set up in a way that it constructs a network that we call the Circle of Willis o Located near base of brain (inferior surface) o Formed by cross-brain arterial connections o Allows for redundancy= often there is more than one artery supplying a portion of the brain so that if something does go wrong and one of these pathways is blocked or disrupted, the brain is still receiving blood, and therefore oxygen, and survives. o In this way the Circle of Willis and therefore the vascular system is a safety mechanism

Function:  Arteries: nourishment—supply of oxygen, nutrients  Veins: waste disposal Pathology  Cerebrovascular accidents (CVAs)  The associated pathology is referred to collectively as cerebrovascular accidents. These refer to any processes that disrupt the flow of blood to the brain, whether via a blockage of an artery or via a rupturing of an artery, for example.  you may relate by understanding that often CVAs are referred in lay terms to a stroke. Distribution of Major Cerebral Arteries:  If we map the distribution routes of some of the major branches of the arteries, this is what you’ll see.  Important to understand, since the vascular system supplies the entire brain with blood and therefore the point where blood flow is disrupted determines what symptoms you will see.  E.g.) If it is the anterior cerebral artery that is blocked, you may see speech or movement difficulties, which with the posterior cerebral artery you will instead see dizziness or double vision. I...