Essay Questions – Exam 3 – Flashcards

The sensory (afferent) nervous system is responsible for receiving sensory information from receptors and transmitting this information to the CNS which means they are responsible for input. Contains both PNS and CNS components: Nerves of the PNS transmit sensory information, and certain parts of brain and spinal cord in CNS interpret this information. Has two components: somatic sensory and visceral sensory. Somatic sensory components are general somatic senses—touch, pain, pressure, vibration, temperature, and proprioception (sensing the position or movement of joints and limbs)—and the special senses (taste, vision, hearing, balance, and smell). Functions considered voluntary because we have some control over them and we tend to be conscious of them. The visceral sensory components transmit nerve impulses from blood vessels and viscera to the CNS (input). The visceral senses include temperature and stretch (of muscles of the organ wall). Functions are said to be involuntary because most of the time you do not have voluntary control over them and are not conscious of them but may become aware of visceral sensations when they are extreme—for example, if you have eaten too much and your stomach is bloated.

The motor (efferent) nervous system is responsible for transmitting motor impulses from the CNS to muscles or glands so it is responsible for output. Contains both CNS and PNS components: Parts of the brain and spinal cord (CNS) initiate nerve impulses, which travel through motor nerves which then transmit these impulses to effector organs. The motor division is subdivided into somatic motor and autonomic motor components. Somatic motor component (somatic nervous system) conducts nerve impulses from the CNS to the skeletal muscles, causing them to contract and is considered voluntary because we have conscious control our skeletal muscles. The autonomic motor component (autonomic nervous system (ANS)) innervates internal organs and regulates smooth muscle, cardiac muscle, and glands without our control, it is also known as the visceral motor system or the involuntary nervous system. For example, we cannot voluntarily make our hearts stop beating, nor can we prevent our stomachs from growling. The autonomic nervous system has two further subdivisions: parasympathetic helps you conserve energy (functions by rest and digest) and sympathetic helps you consume lots of energy when you are under an intense activity or experience. (fight or flight - is active when you are under intense ).

CSF Formation Cerebrospinal fluid is formed by the choroid plexus in each ventricle. THe Choroid plexus is composed of a layer of ependymal cells and the cappillaries in the pia mater. It is produced by a secretion of a fluid from the ependymal cells that originates from the blood plasma. CSF is somewhat similar to blood plasma, but ion concentraions are different in the two. Functions with buoyancy (helps brian float and not become crushed), protection (helps slow movement of brain so brain wont bounce around from sudden forceful movements of the head), environmental stability (remove waste and transport nutrients).

The choroid plexus produces CSF at a rate of about 500 milliliters per day. The CSF circulates through and eventually leaves the ventricles and enters the subarachnoid space, where the total volume of CSF ranges between 100 mL and 160 mL. That means excess CSF is continuously removed from the subarachnoid space so the fluid will not accumulate and compress and damage the nervous tissue. Fingerlike extensions of the arachnoid mater project through the dura mater into the dural venous sinuses to form arachnoid villi (shaggy hair). Collections of arachnoid villi form arachnoid granulations. Excess CSF moves across the arachnoid mater membrane at the arachnoid villi to return to the blood within the dural venous sinuses. Within the subarachnoid space, cerebral arteries and veins are supported by the arachnoid trabeculae and surrounded by cerebrospinal fluid.

1. CSF is produced by the choroid plexus in each ventricle. 2. CSF flows from lateral ventricles and third ventricle through cerebral aqueduct into the fourth ventricle. 3. Most CSF in fourth ventricle flows into the subarachnoid space by passing through openings in the roof of the fourth ventricle. Ventricular openings are the paired lateral apertures and the single median aperture. CSF also fills central canal of the spinal cord. 4. As CSF travels through subarachnoid space, CSF removes waste products and provides buoyancy for the brain and spinal cord. 5. As CSF accumulates within subarachnoid space, it exerts pressure within arachnoid villi. This pressure exceeds the pressure of blood in the venous sinuses. Thus, the arachnoid villi extending into the dural venous sinuses provide a pathway for a one-way flow of excess CSF to be returned into the blood within the dural venous sinuses.

The Nervous tissue is protected from the general circulation by the blood-brain barrier, which strictly regulates what substances can enter the interstitial fluid of the brain. The blood-brain barrier keeps the neurons in the brain from being exposed to drugs, waste products in the blood, and variations in levels of normal substances that could adversely affect brain function. The capillary endothelial cells, astrocyte perivascular feet and continuous basement membrane of the BBB are all significant barriers.The perivascular feet of astrocytes cover, wrap around, and completely envelop capillaries in the brain. Tight junctions between adjacent endothelial cells reduce capillary permeability and prevent materials from diffusing across the capillary wall. The astrocytes act as "gatekeepers" that permit materials to pass to the neurons after leaving the capillaries. The perivascular feet and the brain capillaries are the cellular structures that strictly controls what enters the nervous tissue and are less "leaky" then other cappilaries in the body. Even so, the barrier is not absolute. Usually only lipidsoluble (dissolvable in fat) compounds, such as nicotine, alcohol, and some anesthetics (very beneficial for people in critical condition and needs surgery), can diffuse across the endothelial plasma membranes and into the interstitial fluid of the CNS to reach the brain neurons. The blood-brain barrier is markedly reduced or missing in three distinct locations in the CNS: the choroid plexus, the hypothalamus, and the pineal gland. The reasons for this are that the capillaries of the choroid plexus must be permeable to produce CSF, while the hypothalamus and pineal gland produce some hormones that must have ready access to the bloodstream.