Nervous System 3

Define and explain the steps of cerebellar processing.

Cerebellar processing: the process by which your cerebellum compares motor output regarding desired movment with sensory input regarding your position and makes adjustments to your movement in order to coordinate it. 1. When you want to move, your premotor cortex sends information to your primary motor cortex about the desired movement . 2. The primary motor cortex motor impulses down through the brain stem to the body part you want to move. 3. Some of the motor information is diverted, however, as some of the motor neurons synapse in the pons and are diverted to the cerebellum. 4. This information tells the cerebellum that you want to move or are currently moving a part of your body. 5. At the same time, some of the sensory information travelling up through the spinal cord on its way to the thalamus (which diverts it to the appropriate area of the brain) is diverted to the cerebellum after some afferent neurons synapse in the olivary nucleus of the medulla oblongata. The result is that the cerebellum is able to compare your desired movement with cutaneous sensation to determine if your current body position is conductive to performance of movement. 6. Before the cerebellum allows you to perform the proposed movement (by allowing all motor information to travel directly to the body), it sends information to the motor cortex and brain stem nuclei to tweak the desired movement so that it is physically possible (that is, if the movement needs tweaking; if it doesn't, the movement is allowed to occur). 7. The motor cortex then tells your body to perform the desired movement. USING BOTH MOTOR AND SENSORY INFORMATION TO ENABLE YOU TO PLAN HOW TO PERFORM A MOVEMENT IS CALLED INTEGRATION OF INFORMATION!

Define Paralysis

Loss of motor movement

Define Parathesias

Loss of sensation; often described as a numb or tingling sensation.

Paraplegia/Quadraplegia

Occurs when there is complete cross sectioning or damage to spinal cord. Damage in lower areas (T1-L1) results in paraplegia. Damage in higher areas (cervical vertebrae) results in quadraplegia.

Define Spastic paralysis

Primary motor neurons in the cortex are damaged so that the spinal reflexes remain. Therefore, the antagonists are activated but not the prime movers causing altered body position

Describe the Brain Stem

The brain stem is inferior to the diencephalon. It contains 3 main regions - midbrain, pons, medulla oblongata. It has grey matter/nuclei on the inside and white matter on the outside. It contains pathways for neuron tracts to communicate with the spinal cord. It connects the brain with the spinal cord and is essential for survival. It controls many primitive automatic responses such as elevated heart rate and breathing rate when scared. It contains nuclei of 10/12 cranial nerves. That is why, to test for brain death or for damage to one hemisphere, cranial nerve testing is performed. This is because, when a person is brain dead, their brain stem doesn't function.

Describe the Cerebellum

The cerebellum is inferior and posterior to the cerebrum/cortex. It has two hemispheres with 3 lobes in each hemisphere - anterior, posterior and flocculonodular lobes. Its two hemispheres are joined by the vermis. It is responsible for subconscious coordination of movement. Not all the motor fiber tracts travel directly from the cortex to the spinal cord. Some synapse in the nuclei of the pons and are taken to the cerebellum. Similarly, not all afferent neurons travel from the spinal cord to the cortex because some are diverted to the cerebellum after synapsing in the inferior olivary nucleus of the medulla oblongata. This allows the cerebellum to compare motor information about what you want to do or are doing with sensory information to tell you if you are in the right place at the right time to do it.

Limbic (ring) system

The limbic system is responsible for generating emotional responses. It starts at the amygdala, which is responsible for recognizing angry/fearful expressions and stimulates the fear response after visual information regarding something fearful is sent to it from the visual association cortex. Information from the amygdala then courses around the limbic ring (particularly the cingulate gyrus), which is in close proximity to nearly every centre in the brain and so influences many things (your ability to run, heightened sense to the danger (sensory cortex), multimodal association areas in the frontal lobe that assist in making complex decisions on what you will do next). The limbic ring ends at the hypothalamus, which generates an increase in heart rate and breathing rate if the information is fearful. SOME NTS ARE RELEASED FROM THE LIMBIC RING INCLUDING NOREPINEPHRINE.

Describe the medulla oblongata.

The medulla oblongata controls many SUBCONCIOUS, REGULATORY AFFAIRS. The messages to regulate these processes originally comes from the hypothalamus. Neurons from the hypothalamus synapse in the medulla oblongata, which sends the information to the body. The medulla oblongata essentially keeps you alive. It contains the decussation of pyramids, or the point where pyramidal/corticospinal motor tracts from the cortex cross over so that fibers from the right hand side of the brain control the left hand side of the body and visa versa. It contains the 4th ventricle and inferior cerebellar peduncles. It blends into the spinal cord at the foramen magnum. The medulla oblongata contains the inferior olivary nucleus, the point where afferent neurons coming up the spinal cord synapse before being taken to the cerebellum. So, the cerebellum is able to compare motor output (pons) with sensory input (medulla oblongata), which is very important for coordination. Information about balance from the vestibule also travels to the medulla oblongata's vestibular nuclear complex (VIII) before being sent to the sensory cortex by the thalamus. It contains a cochlear nucleus, which is related to hearing. When you are knocked unconscious and your cortex doesn't function properly, it is your medulla oblongata that keeps you alive by keeping your heart beating and your breathing regular. It sends motor neurons to the diaphragm to make you breathe diaphragmatically (long, spaced breaths) instead of intercostally when you are unconscious. It maintains your body's homeostasis. It contains motor nuclei including a cardiovascular centre (controls rate and force of heart beat), respiratory centre (controls rate, depth and rhythm of breathing) and a vasomotor centre (controls blood vessel diameter, which impacts on blood pressure). It also contains other cetres which control vomiting, swallowing, sneezing, coughing and hiccupping.

Describe the Midbrain

The midbrain is a connecting point. It is the point of connection of the diencephalon with the brain stem. It contains two cerebral peduncles, which are white matter tracts (axons) composed of pyramidal motor fiber tracts. If damaged, one might have problems with movement. The midbrain also contains nuclei. It contains four dome-shaped bodies on its posterior aspect called the corpora quadrigemina. The corpora quadrigemina are responsible for coordinating sensation with movement (like the multimodal association areas!). They are relay stations for some cranial nerves. They are also responsible for the startle reflex - turning your head towards a loud, sudden sound. Sensory information from the ear is taken to the midbrain where it immediately synapses with a motor neuron that innervates a neck muscle. This results in your head being turned when you hear a loud sound. The inferior colliculi are auditory relay stations. The midbrain also contains the substantia nigra, which are dark regions in the midbrain, consisting of melanin-containing cell bodies and dopamine. Degeneration of the substantia nigra leads to Parkinson's disease. The substantia nigra is a relay station for movement and coordinates smooth movement.

Describe the Pons

The pons is a bridge connecting the midbrain with the medulla oblongata. It also connects the cerebellum to the brain stem via its superficial, transverse fibers and cerebellar peduncles. It has white matter on the outside and grey matter on the inside. It allows communication between the left and right hemispheres of the cerebellum. Motor neurons travelling to the cerebellum synapse in nuclei in the pons. The pons also contains motor fiber tracts travelling to the spinal cord (longitudinal fibers). The deep pontine nuclei of the pons project facial, trigeminal and abducens nerves. Therefore, damage to the pons can result in damage of the nerves and function of the face and throat.