In these review lectures, we will discuss the nervous system. As a nurse, you will practice in varied settings where patients may have altered neurologic function. Nurses must be skilled in the general assessment of neurologic function.
This requires knowledge of the anatomy and physiology of the nervous system. The human nervous system is a highly specialized system responsible for the control and integration of the body's maniacal nervous system. activities.
It controls motor, sensory, autonomic, cognitive, and behavioral activities. The nervous system can be divided into the central nervous system and the peripheral nervous system. The central nervous system has the brain and spinal cord.
The peripheral nervous system includes the cranial and spinal nerves and the autonomic and somatic systems. The basic functional unit of the nervous system is the neuron. Neurons are supported, protected, and nourished by glial cells. Neurons communicate with one another using neurotransmitters. They can also communicate with other tissues using neurotransmitters.
Neurotransmitters can potentiate, terminate, or modulate a specific action or can excite or inhibit a target cell. That means... Some neurotransmitters are excitatory and some are inhibitory.
Many neurologic disorders are caused by an imbalance in neurotransmitters. So how do these neurons talk with each other or other tissues? Well, the neuron is composed of dendrites that branch out to receive these electrochemical messages.
Dendrites bring information to the cell body. The axon is a long projection that carries impulses away from the cell body. Some of these axons are myelinated, and that increases the speed of conduction.
Impulses travel down an axon to the synaptic terminal. Neurotransmitters are carried to the presynaptic membrane and are released into the cleft. They diffuse across the cleft and bind with the receptor, causing a response. All brain functions are modulated through neurotransmitter receptor activity, including memory and other cognitive processes. So remember, the central nervous system contains some really important things, like the brain and the spinal cord, which has all those neurons.
So what protects the central nervous system? The brain is contained in a rigid skull, a bony structure that protects the brain from trauma. The bony skull protects the brain from external trauma. It is composed of 8 cranial bones and 14 facial bones.
The foramen magnum is the largest hole in the skull through which the brain stem extends to the spinal cord. This foramen offers the only major space for the expansion of the brain contents when intracranial pressure occurs. The bones of the vertebral column surround and protect the spinal cord and normally consist of seven cervical, 12 thoracic, and five lumbar vertebrae. I always remember these as breakfast at 7 a.m., lunch at noon, and dinner at 5. There's also the sacrum which are a fused mass of five vertebrae and they terminate in the coccyx which are four fused vertebrae. The vertebrae are also separated by intervertebral discs.
The meninges are three layers of protective membranes that surround the brain and spinal cord. They provide protection, support, and nourishment. I remember they PAD, pad the brain. The pia mater, the innermost layer, is thin and transparent.
and it hugs the brain closely and extends into every fold of the brain surface. The arachnoid mater, the middle membrane, is thin, it's delicate, and it closely resembles a spider web, hence the name arachnoid. In the subarachnoid space, the space below the arachnoid layer, is where the cerebral spinal fluid lives.
All cerebral arteries and veins lie in this space. The dura mater, forms the outermost layer. It is tough, thick, inelastic, and fibrous. Cerebral spinal fluid circulates within that subarachnoid space that surrounds the brain, brain stem, and spinal cord. This fluid provides cushioning for the brain and spinal cord, and it also carries nutrients.
The brain literally floats in CSF. CSF should always be clear, colorless, and watery. There is approximately 100 to 200 milliliters of CSF.
total volume at all times. The CSF is formed continuously by the ventricles in the brain. It is reabsorbed by the arachnoid villi in the ventricles at the same rate at which it is formed. These are not the ventricles that are in the heart.
These are the ventricles in the brain, the four fluid-filled cavities within the brain that connect with one another and the spinal canal. This graphic shows you how the CSF is made in the ventricles and it circulates around the surface of the brain in that subarachnoid space and in the spinal cord. CSF is important in immune and metabolic functions in the brain. About 500 milliliters is made per day.
It is similar in composition to plasma. It can be sampled through a process called lumbar puncture or intraventricular catheter. The brain does not store nutrients and requires a constant supply of oxygen. The brain receives 15% of cardiac output at all times, or about 750 milliliters per minute.
The arterial cerebral blood supply arises from the common carotid artery. These branch into many different arteries. These become important when a patient has a stroke.
Based on what artery has been affected, leads to different symptoms. Anterior cerebral arteries supply the medial and interior portions of the frontal lobe. Middle cerebral arteries supply the outer portions of the frontal and the parietal and superior temporal lobes.
Posterior cerebral arteries supply the medial portion of the occipital and the inferior temporal lobes. The circle of Willis or cow provides collateral circulation. So if one of the arteries becomes blocked or narrowed, others can often preserve circulation to prevent ischemia and it allows blood to be directed on demand.
Unfortunately, because of its shape, it is prone to forming aneurysms. The venous flow out of the brain is provided through the internal jugular veins, and gravity is important for venous flow. The blood-brain barrier protects the brain from certain potentially harmful agents, while allowing nutrients and gases to enter.
If you're like me, when I first started learning about the blood-brain barrier, I always thought of it as something in the neck somewhere. It had to be something that prevented... anything bad from getting up to the brain. But that's not the case. It is actually a physiologic barrier between blood capillaries and brain tissue.
It is formed by the endothelial cells of the brain's capillaries, which form continuous tight junctions, creating a barrier to macromolecules and many compounds. The structure of brain capillaries differs from that of other capillaries. Some substances that normally pass readily into most tissues are prevented from entering brain tissue. This brain barrier can be altered by trauma, cerebral edema, and cerebral hypoxemia.
This is the end of part one. I look forward to sharing more about the anatomy of the nervous system in the next lecture.