ANAPHY: LESSON 6 - NERVOUS SYSTEM

AMO INI AN USA HA MAKURI NA LESSON

1. Receiving sensory input

2. Integrating information

3. Controlling muscles and glands

4. Controlling muscles and glands

5. Establishing and maintaining mental activity

major functions of the nervous system

Receiving sensory input

Sensory receptors monitor numerous external and internal stimuli. We are aware of sensations from some stimuli and other stimuli that are processed at a subconscious level.

Integrating information

The brain and spinal cord process sensory input and initiate responses, which can be immediate, stored as memory, or ignored.

Controlling muscles and glands

The nervous system controls skeletal muscles, cardiac muscle, smooth muscle, and glands, allowing it to control movements and bodily functions.

Maintaining homeostasis

The nervous system helps maintain a constant internal environment by detecting, interpreting, and responding to changes in internal and external conditions.

Establishing and maintaining mental activity

The brain is responsible for mental activities such as consciousness, memory, and thinking.

1. central nervous system

2. peripheral nervous system

nervous system can be divided into two major divisions:

Central Nervous System (CNS)

consists of the brain and spinal cord, which are major organs for processing sensory input and initiating responses.

Peripheral Nervous System (PNS)

consists of all the nervous tissue outside the CNS, including nerves and ganglia

Peripheral Nervous System (PNS)

functions to link the CNS with various parts of the body.

1. Sensory Division

2. Motor Division

Peripheral Nervous System (PNS) can be subdivided into two parts

Sensory division

or afferent division

Sensory division

conducts action potentials from sensory receptors to the CNS.

sensory neurons

neurons that transmit action potentials from the periphery to the CNS.

Motor division

or efferent division

Motor division

conducts action potentials from the CNS to effector organs, such as muscles and glands.

motor neurons

neurons that transmit action potentials from the CNS toward the periphery

1. Somatic nervous system

2. Autonomic nervous system

motor division can be further subdivided based on the type of effector being innervated:

Somatic nervous system

transmits action potentials from the CNS to skeletal muscles.

Autonomic nervous system (ANS)

transmits action potentials from the CNS to cardiac muscle, smooth muscle, and glands.

1. sympathetic divisions

2. parasympathetic divisions

autonomic nervous system is divided into

Sympathetic division

the division of the ANS that prepares the body for stressful situations and activates the "fight or flight" response.

Parasympathetic division

The division of the ANS that promotes relaxation and conserves energy.

Enteric nervous system (ENS)

is a unique subdivision of the peripheral nervous system. It has both sensory and motor neurons contained wholly within the digestive tract.

Enteric nervous system (ENS)

It can function without input from the CNS or other parts of the PNS, although it is normally integrated with the CNS by sensory neurons and ANS motor neurons.

Neurons

or nerve cells that receive stimuli, conduct action potentials, and transmit signals to other neurons or effector organs.

1. Cell body

2. dendrites

3. Axon

Parts of neurons

cell body

contains a single nucleus. It is the source of information for gene expression.

Dendrites

are short, often highly branching cytoplasmic extensions that are tapered from their bases at the neuron cell body to their tips.

Dendrites

usually receive information from other neurons or from sensory receptors and transmit the information toward the neuron cell body.

axon

a single long cell process extending from the neuron cell body.

axon hillock

The area where the axon leaves the neuron cell body.

collateral axons

branches of axons

myelin sheath

Axons can be surrounded by a highly specialized insulating layer of cells called the

1. Multipolar neurons

2. Bipolar neurons

3. Pseudo-unipolar neurons

Types of Neurons

Multipolar neurons

have many dendrites and a single axon. This kind of neurons are mostly found within the CNS and nearly all motor neurons.

Bipolar neurons

have two processes: one dendrite and one axon. They are located in some sensory organs

Pseudo-unipolar neurons

have a single process extending from the cell body. It appears to have a single axon. Most other sensory neurons are made out of this kind of neurons.

Pseudo-unipolar neurons

This neuron divides into two processes: one process extends to the periphery, and the other extends to the CNS.

Glial cells

or neuroglia, are supportive cells of the CNS and PNS that do not conduct action potentials. They carry out different activities that enhance neuron function and maintain normal conditions within nervous tissue.

1. astrocytes

2. ependymal cells

3. microglia

4. oligodendrocytes

Types of glial cells in the central nervous system

1. Schwann cells

2. satellite cells

Types of glial cells in the peripheral nervous system

Astrocytes

are the major supporting cells in the CNS and play a role in signaling activity, forming the blood-brain barrier, and limiting damage to neural tissue.

blood-brain barrier

a permeability barrier between the blood and the CNS.

Ependymal cells

Ependymal cells line fluid-filled cavities within the CNS. It produce cerebrospinal fluid, and help move it through the CNS.

Microglia

Microglia act as immune cells of the CNS, protecting the brain by removing bacteria and cell debris.

Oligodendrocytes

In the CNS, it provide an insulating material that surrounds axons

Schwann cells

In the PNS, it provide an insulating material that surrounds axons

Satellite Cells

found around the cell bodies of certain neurons of the PNS. It provides support and nutrition to the neurons and protects it from heavy-metal poison.

Myelin sheaths

are specialized layers formed by oligodendrocytes in the CNS and Schwann cells in the PNS that wrap around axons, preventing ion movement and increasing the speed of action potentials.

myelinated axons

Axons with these myelin sheaths

Gaps in the myelin sheath

nodes of Ranvier

Unmyelinated axons

lack the myelin sheaths; however, these axons rest in indentations of the oligodendrocytes in the CNS and the Schwann cells in the PNS

Gray matter

consists of groups of neuron cell bodies and dendrites, with very little myelin, found in the cortex of the brain and nuclei within the brain.

cortex

in the CNS, it is the gray matter on the surface of the brain

nuclei

in the CNS, it is the clusters of gray matter located deeper within the brain

ganglion

In the PNS, it is a cluster of neuron cell bodies

White matter

Consists of bundles of parallel axons with myelin sheaths, forming nerve tracts or conduction pathways.

nerve tracts

or conduction pathways, which propagate action potentials from one area of the CNS to another.

nerves

In the PNS, they are formed through the bundles of axons and associated connective tissue

Resting membrane potential

The uneven distribution of charge across the cell membrane, with the inside being negatively charged compared to the outside.

Leak channels

Ion channels that are always open, allowing ions to "leak" across the membrane down their concentration gradient.

Gated channels

Ion channels that are closed until opened by specific signals

voltage-gated channels

opened by a change in membrane potential.

Generation of the Resting Membrane Potential

1. action potentials

2. action potential conduction

3. synapse

3 stages of neuron transmission

Action potential

A rapid change in the membrane potential of excitable cells, caused by the opening and closing of voltage-gated Na+ and K+ channels.

Action potential conduction

The propagation of action potentials along the cell membrane, either through continuous conduction in unmyelinated axons or saltatory conduction in myelinated axons.

1. continuous conduction

2. saltatory conduction

Pattern of action potential conduction along a neuron cell may occur in one of two ways:

continuous conduction

occurs in unmyelinated axons. An action potential in one part of a cell membrane stimulates local currents in adjacent parts of the cell membrane. The local currents in the adjacent membrane produce an action potential. The action potential is conducted along the entire axon cell membrane.

saltatory conduction

In myelinated axons, an action potential at one node of Ranvier causes a local current to flow through the surrounding extracellular fluid and through the cytoplasm of the axon to the next node, stimulating an action potential at that node of Ranvier. By this means, action potentials “jump” from one node of Ranvier to the next along the length of the axon.

Synapse

A junction where the axon of one neuron interacts with another neuron or with cells of an effector organ, such as a muscle or gland.

1. presynaptic terminal

2. postsynaptic membrane

3. synaptic cleft

3 major components of the structure if a synapse

Presynaptic terminal

The end of the axon that forms a synapse, where neurotransmitters are released.

Postsynaptic membrane

The membrane of the dendrite or effector cell that receives the neurotransmitters from the presynaptic terminal.

Synaptic cleft

The space separating the presynaptic and postsynaptic membranes.

Neurotransmitters

Chemical substances stored in synaptic vesicles in the presynaptic terminal, released into the synaptic cleft to bind to specific receptor molecules on the postsynaptic membrane.

Neurotransmitter

Chemical substances that transmit signals across synapses between neurons.

Hyperpolarized

A state in which the membrane potential of a cell becomes more negative than the resting membrane potential, inhibiting the occurrence of an action potential.

Acetylcholine (ACh)

A neurotransmitter substance involved in synaptic transmission, particularly in the neuromuscular junction.

Norepinephrine

A neurotransmitter substance that can be actively transported back into the presynaptic terminal or broken down by enzymes.

Acetylcholinesterase

An enzyme that breaks down acetylcholine, particularly in synapses where acetylcholine is the neurotransmitter.

1. Converging pathway

2. Diverging pathway

2 simplest neuronal pathways

Converging pathway

A neuronal pathway in which two or more neurons synapse with the same neuron, allowing information from multiple pathways to converge into a single pathway.

Diverging pathway

A neuronal pathway in which the axon from one neuron divides and synapses with more than one other neuron, allowing information from one pathway to diverge into multiple pathways.

Summation

The process of integrating multiple sub-threshold local potentials in neuronal pathways to bring the membrane potential to threshold and trigger an action potential.

1. Spatial Summation

2. 2. temporal summation

2 types of summation

Spatial summation

occurs when the local potentials originate from different locations on the postsynaptic neuron— for example, from converging pathways.

occurs when local potentials overlap in time. This can occur from a single input that fires rapidly, which allows the resulting local potentials to overlap briefly.

Temporal summation

Central Nervous System (CNS)

The brain and spinal cord, which are responsible for processing and coordinating information.

brain

housed within the skull

spinal cord

in the vertebral column

Peripheral Nervous System (PNS)

All the nerves and ganglia outside the brain and spinal cord that collect and relay information to the CNS and regulate activity in muscles and glands.

1. 12 pairs of cranial nerves

2. 31 pairs of spinal nerves

nerves of the PNS can be divided into two groups

extends from the foramen magnum at the base of the skull to the second lumbar vertebra

spinal cord

Spinal cord

The part of the CNS that is housed within the vertebral column and is responsible for relaying information between the body and the brain.

Cauda Equina

The collective term for the inferior end of the spinal cord and the spinal nerves exiting there, resembling a horse's tail.

1. Dorsal Columns

2. Ventral Columns

3. Lateral Columns

white matter in each half of the spinal cord is organized into three columns:

Dorsal Columns

The organized white matter columns in the spinal cord located on the posterior side.

Ventral Columns

The organized white matter columns in the spinal cord located on the anterior side.