LBBBIO7 LE 1 | Topic 4: Nervous System

Nervous System

- The most complex system in the body

- Formed by a network of many billion nerve cells (neurons), all assisted by many more supporting cells glial cells

CNS and PNS

two major structural divisions of the nervous system

CNS

consists of the brain (cerebrum and cerebellum) and spinal cord

PNS

composed of the cranial, spinal, and peripheral nerves conducting impulses to and from the CNS (sensory and motor nerves, respectively) and ganglia that are small aggregates of nerve cells outside the CNS

dura mater, arachnoid mater, and pia mater

3 layers of the meninges

dura mater

outermost meningeal layer, a tough, strong, and thick layer of dense connective fibers

arachnoid mater

- a more delicate connective tissue, deep to the dura mater

- along with the dura mater, it surrounds the brain and spinal cord on their external surfaces.

pia mater

- The innermost meningeal layer

- This layer contains numerous blood vessels and adheres directly to the surfaces of the brain and spinal cord.

subarachnoid space

- the space between the arachnoid mater and the pia mater

- contains cerebrospinal fluid (CSF) that bathes and protects both the brain and spinal cord.

cerebrospinal fluid (CSF)

a clear, colorless fluid that cushions the brain and spinal cord, and gives them buoyancy as a means of protection from physical injuries.

choroid plexuses

The CSF is continually produced by the _____________ in the lateral, third, and fourth ventricles, or cavities, of the brain.

sensory (afferent) division and motor (efferent) division

two major sensory divisions of the nervous system

somatic division

sensory division involving sensory input perceived consciously (e.g., from eyes, ears, skin, and musculoskeletal structures)

visceral division

sensory division involving sensory input not perceived consciously (e.g.,, from internal organs and cardiovascular structures)

somatic division

motor division involving motor output controlled consciously or voluntarily (e.g., by skeletal muscle effectors)

autonomic division

motor division involving motor output not controlled consciously (e.g., by heart or gland effectors)

sensory neurons

neurons that transmit information from the body's senses and internal environment to the central nervous system (CNS)

motor neurons

neurons that transmit commands from the CNS to muscles, glands, and organs to produce a response

neurons

The functional unit in both the CNS and PNS.

cell body/perikaryon/soma

contains the nucleus and most of the cell's organelles and serves as the synthetic or trophic center for the entire neuron

dendrites

the numerous elongated processes extending from the perikaryon and specialized to receive stimuli from other neurons at unique sites called synapses

axon

- a single long process ending at synapses specialized to generate and conduct nerve impulses to other cells (e.g., nerve, muscle, and gland cells)

- may also receive information from other neurons, information that mainly modifies the transmission of action potentials to those neurons

multipolar neurons

neurons with one axon or two or more dendrites; the most common.

bipolar neurons

neurons that have one dendrite and one axon, comprise the sensory neurons of the retina, the olfactory epithelium, and the inner ear

unipolar or pseudounipolar neurons

neurons that have a single process that bifurcates close to the perikaryon, with the longer branch extending to a peripheral ending and the other towards the CNS

anaxonic neurons

neurons that have many dendrites but no true axon, do not produce action potentials, but regulate electrical changes of adjacent CNS neurons

neuroglia

the highly branched, supportive, nonneuronal cells in the CNS that surround the neurons, their axons and dendrites.

astrocytes, oligodendrocytes, microglia, and ependymal cells

types of neuroglia in CNS

schwann and satellite cells

types of neuroglia in PNS

astrocytes

- Are the largest and most numerous in gray matter

- Consists of two types, fibrous and protoplasmic

- Form glial limiting membrane that surrounds the brain and spinal cord

- Support metabolic exchange and contribute to energy metabolism of CNS

- Control chemical environment around neurons by clearing neurotransmitters

oligodendrocytes

- Surround and myelinate numerous axons at one time, in contrast to Schwann cells

- It produces myelin, an insulating lipid-rich sheath that wraps around axons to protect them and dramatically increase the speed of nerve impulse transmission via saltatory conduction

nodes of Ranvier

Each oligodendrocyte can myelinate multiple axons, leaving periodic ____________ where sodium channels are concentrated, allowing the electrical impulse to "jump" between segments

microglia

- Parts of the mononuclear phagocyte system and found throughout CNS

- Phagocytic cells in the CNS, similar to connective tissue macrophages

ependymal cells

- Line the ventricles in the brain and central canal of the spinal cord

- Ciliated cells move the CSF through the central canal of spinal cord

schwann cells

- glial cells in the peripheral nervous system (PNS) that provide support to neurons

- Their main function is to form the myelin sheath, a fatty insulation that wraps around axons, increasing the speed of nerve signal conduction

satellite cells/satellite glial cells (SGCs)

- flattened cells in the peripheral nervous system that surround neuron cell bodies in sensory, sympathetic, and parasympathetic ganglia, forming a protective sheath or "neuron-glial unit"

- they are vital for maintaining the neuronal microenvironment, supporting neuron health by supplying nutrients and regulating the extracellular space.

gray matter

- the matter that contains neuron cell bodies and dendrites responsible for processing information

- its color comes from the high concentration of cell bodies

- located on the outside, forming the cerebral cortex

white matter

- the matter that consists of myelinated axons that transmit signals between regions

- its color comes from the fatty myelin sheath surrounding the axons, which speeds up nerve signal transmission

- located in the inside

cerebrum

- The largest part of the brain, making up most of its mass

- Divided into 2 hemispheres (left and right) connected by the corpus callosum. It also has an outer layer of gray matter called the cerebral cortex, which is highly folded.

- Interprets sensory input, controls conscious thought and memory, directs voluntary movements, and is responsible for emotions, speech, and personality.

cerebellum

- The portion of the brain in the back of the head between the cerebrum and the brain stem.

- Coordinates precise muscle movements, maintains balance and posture, supports motor learning, and contributes to speech, emotion, and decision-making.

medulla oblongata

the lowest part of the brainstem that connects to the spinal cord and controls vital involuntary functions like breathing, heart rate, and blood pressure, as well as reflex actions such as swallowing and coughing

spinal cord

long, tube-shaped structure of nerve tissue that extends from the brainstem down the back, protected by the vertebral column

medullated nerve

- a nerve fiber covered in a myelin sheath, a fatty insulating layer that speeds up the transmission of electrical signals

- crucial for rapid and efficient communication within the nervous system, found in both the peripheral and central nervous system

Nodes of Ranvier

Its primary function is to propagate electrical signals (action potentials) along a myelinated axon by allowing ions to flow through protein channels at these gaps in the myelin sheath.

saltatory conduction

this process enables the signal to "jump" from one node to the next, significantly increasing the speed and efficiency of nerve impulse transmission throughout the nervous system

motor nerve endings

- the terminal branches of motor neuron axons that transmit signals to muscle fibers, leading to muscle contraction

- form synapse called the neuromuscular junction, where the neurotransmitter acetylcholine is released to trigger an electrical signal and subsequent muscle action

acetylcholine

neurotransmitter released by the neuromuscular junction to trigger an electrical signal and subsequent muscle action