Nervous system

Reflex

Automatic, subconscious response to stimuli within or outside the body

Parts of a reflex arc: Effector

A muscle or gland Function: Responds to stimulation by the motor neuron and produces the reflex or behavioral action

Third Ventricle

A narrow space in the midline of the brain beneath the corpus callosum (a bridge of axons that links the two cerebral hemispheres). The third ventricle communicates with the lateral ventricles through openings in its anterior end.

Spinal Cord

A slender column of nervous tissue that is continuous with the brain and extends downward through the vertebral canal. The spinal cord originates where nervous tissue leaves the cranial cavity at the level of the foramen magnum. The cord tapers to a point and terminates near the intervertebral disc that separates the first and second lumbar vertebrae.

Arachnoid Mater

A thin, weblike membrane that does not have blood vessels and is located between the dura and pia maters. It spreads over the brain and spinal cord but does not dip into the grooves and depressions on their surfaces. Many thin strands extend from its under-surface and attach to the pia mater. A subarachnoid space between the arachnoid and pia maters contains the clear, watery, cerebrospinal fluid (CSF).

Sensory Receptor

All reflexes share the same basic components, which together are known as the reflex arc. A reflex arc begins with a sensory receptor at the dendritic end of a sensory neuron. Impulses on these sensory neurons enter the CNS and constitute a sensory or afferent limb of the reflex. The CNS is a processing center. Afferent neurons may synapse with interneurons, which may in turn connect with other parts of the CNS. Afferent neurons or interneurons ultimately connect with motor neurons, whose fibers pass outward from the CNS to effectors.

What do ependymal cells in the choroid plexuses do?

Block passage of water soluble substances between the blood and CSF. (blood-CSF barrier) Selectively transfer certain substances from teh blood into the CSF by facilitated diffusion and transfer other substances by active transport, regulating the CSF composition.

What is CSF?

CSF is a clear, viscid liquid that differs in composition from the fluid that leaves the capillaries in other parts of the body. It contains a greater concentration of sodium and lesser concentrations of glucose and potassium than do other extracellular fluids.

What is the function of CSF?

CSF is nutritive and protective. It helps maintain a stable ionic concentration in the CNS and provides a pathway to the blood for waste. The CSF may also supply information about the internal environment to autonomic centers in the hypothalamus and brainstem, because the fluid forms from blood plasma and therefore its composition reflects changes in body fluids.

Where is CSF?

CSF occupies the subarachnoid space of the meninges, so it completely surrounds the brain and spinal cord. In effect, the organs float in the fluid. THe CSF protects the brain and spinal cord by absorbing forces that might otherwise jar and damage their delicate tissues.

Functions of the Spinal Cord

Center for spinal reflexes Pathway for impulses to/from the brain

Refelx Arc

Communication in the nervous system combines a series of action potentials along the axon of a neuron and synaptic transmission between that neuron and postsynaptic cell. Two or more neurons involved in such communication constitute a nerve pathway. The simplest of the nerve pathways begin with a sensory receptor and ends with an effector and involves as few as 2 neurons.

Central Nervous System (CNS)

Consists of the brain and spinal cord

Parts of a reflex arc: Motor neuron

Dendrite, cel body and axon of a motor neuron Function: conducts an impulse from the brain to spinal cord out to the synapse with an effector

Parts of a reflex arc: Interneuron

Dendrite, cell body and axon of a neuron within the brain or spinal cord Function: Serves as processing center; conducts an impulse from the sensory neuron to its synapse with a motor neruon

Parts of a reflex arc: Sensory neuron

Dendrite, cell body, and axon of a sensory neuron. Function: Conducts and impulse from the receptor into the brain or spinal cord

Patellar Reflex

Example of a simple monosynaptic reflex, because it uses only two neurons- a sensory neuron comunicating directly to a motor neruon. St

Falx cerebri

Extends downward into the longitudinal fissure, and separates the right and left cerebral hemispheres.

Ventricles

Four interconnected cavities that lie in the cerebral hemispheres and brainstem. These spaces are continuous with the central canal of he spinal cord and are filled with CSF.

Fourth Ventricle

Located in the brainstem, just anterior to the cerebellum. A narrow canal, the cerebral aqueduct connects it to the third ventricle and passes lenghtwise through the brainstem.

How much CSF do humans secrete daily?

Humans secrete nearly 500 millileters of CSF daily. However, only about 140 mL are in teh nervous system at any time, because CSF is continuously reabsorbed into the blood through tiny, fingerlike structures called arahnoid granulations that project from the sub-arachnoid space into the blood-filled dural sinuses.

Dura Mater

In some regions, the dura mater extends inward between lobes of the brain and forms supportive and protective partitions. In other areas, the dura mater splits in two layers forming channels called dural sinuses. Venous blood flows through these channels as it returns from the brain to vessels leading to the heart.

Meninges

Membranes located between the bone and soft tissues of the nervous system that protect the brain and spinal cord.

Where is most CSF formed?

Most CSF is formed in the lateral ventricles, from where it slowly circulates into the third and fourth ventricles and into the central canal of the spinal cord. It also enters the sub-arachnoid space of the meninges by passing through the wall of the fourth ventricle near the cerebellum.

Reflex Arc (simplified)

Neural pathway, consisting of a sensory receptor, 2 or more neurons, and an effector. Simple reflex arc (contains only sensory and motor neurons) Most common reflex arc (sensory neuron, interneurons, motor neurons)

Dura Mater

Outermost layer of meninges. Composed of tough, WHITE, dense connective tissue and contains many blood vessels and nerves. The dura mater attaches to the inside of the cranial cavity and forms the internal periosteum surrounding skull bones.

Choroid Plexus

Reddish cauliflower-like masses of specialized capillaries from the pia mater that secrete CSF.

Reflexes are...

Reflexes are automatic responses to changes (stimuli) inside or outside the body. THey help maintain homeostasis by controlling many involuntary processes such a s heart rate, breathing rate, blood pressure, and digestion. Reflexes also carry out the automatic actions involved in swallowing, sneezing, coughing, and vomiting.

Where do reflexes occur?

Reflexes occur throughout the CNS. those that involve the spinal cord are called spinal reflexes and reflect the simplest level of CNS function.

Tentorium cerebelli

Separates the occipital lobes of the cerebrum from the cerebellum.

Falx cerebelli

Separates the right and left cerebellar heispheres

Brain and spinal cord

The brain connects to the spinal cord through the brainstem, which allows two-way communication between the CNS and the peripheral nervous system (PNS).

Brain

The brain is the largest, most complex part of the nervous system. The brain includes two cerebral hemispheres (left and right), the diencephalon, the brainstem, and the cerebellum.

Dura Mater

The dura mater continues into the vertebral canals as a strong, tubular sheath that surrounds the spinal cord. It is attached to the cord at regular intervals by a band of pia mater that extends the length of the spinal cord on either side. THe dural sheath terminates as a blind sac at the level of the second sacral vertebra, below the end of the spinal cord. The sheath around the spinal cord is not attached directly to the vertebrae but is separated by an epidural space which lies between the dural sheath and the bony walls. This space contains blood vessels, loose connective tissues, and adipose tissue that pad the spinal cord.

Pia Mater

The pia mater is thin and contains many nerves, as well as blood vessels that nourish the underlying cells of the brain and spinal cord. The pia mater is attached to the surfaces of these organs and follows their irregular contours, passing over high areas and dipping into depressions.

Parts of a reflex arc: Receptor

The receptor end of a dendrite or a specialized receptor cell in a sensory organ. Function: Sensitive to s specific type of internal change

Spinal Nerves

The spinal cord consists of 31 segments, each of which gives rise to a pair of spinal nerves. The spinal nerves branch to various body parts and connect them with the CNS.

Lateral Ventricles

The two largest ventricles, one in each cerebral hemisphere. They extend anteriorly and posteriorly into the cerebral hemispheres.

Ventricles

The ventricles are continuous with the central canal of the spinal cord. There are filled with CSF.

What are arachnoid granulations?

tiny fingerlike structers protruding from the subarachnoid space into the blood filled dural sinuses that reabsorb CSF