Human Nervous System (Part 1) - Spinal Cord and Periphery (Animation)

Summary

This animation delves into the intricacies of the human nervous system, highlighting the central and peripheral components. It explains the roles of nerve cells, spinal nerves, and the synaptic process, including the function of neurotransmitters. The script also explores sensory receptors in the skin and their connection to the spinal cord, illustrating how stimuli are translated into electrical impulses and processed by the brain, culminating in reflex actions.

Takeaways

• 🧠 The human nervous system is a complex network composed of numerous nerve cells that process environmental stimuli.
• 🌐 It is divided into the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS).
• 💛 The CNS is well-protected within the skull and spinal column, while the PNS extends throughout the body, as depicted in yellow in the animation.
• 🦴 The spinal cord is housed within the spinal canal, surrounded by vertebrae, fatty and connective tissue, and is covered by three protective membranes.
• 🔁 The spinal nerves of the PNS connect to the CNS, with afferent fibers carrying impulses to the CNS and efferent fibers carrying impulses to muscles and glands.
• 🔋 Nerve cells, or neurons, consist of a cell body, dendrites, and an axon. Dendrites receive stimuli, while the axon conducts electrical impulses.
• 🔗 At the end of an axon are terminal buttons, which form synapses with other neurons or cells, and are involved in neurotransmitter release.
• 🚀 The conduction speed of impulses is increased by myelination, where Schwann cells wrap around the axon, forming nodes of Ranvier.
• 💊 Neurotransmitters are stored in vesicles within terminal buttons and are released into the synaptic cleft through a process called exocytosis.
• 🔄 The process of synaptic transmission allows nerve cells to communicate with each other, converting neurotransmitters back into electrical impulses at the post-synaptic cell.
• 🔬 Sensory receptors in the skin, such as Meissner's corpuscles, Merkel cells, and Ruffini corpuscles, convert mechanical stimuli into electrical impulses for transmission to the CNS.
• 🔄 The spinal cord processes sensory information and can also facilitate reflex actions, such as muscle contractions, in response to stimuli without brain involvement.

Q & A

What is the human nervous system?

The human nervous system is a complex network composed of countless nerve cells that process stimuli from the environment and control various functions such as movement, sensation, and cognition.

How is the nervous system divided?

The nervous system is divided into the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which extends throughout the body.

What are the main components of the CNS?

The CNS is primarily composed of the brain and spinal cord, which are well protected by the skull and spinal column, respectively.

What is the role of the peripheral nervous system in the body?

The PNS is responsible for transmitting nerve impulses from various parts of the body to the CNS and from the CNS to the muscles and glands.

What are the different types of nerve fibers in the PNS?

The PNS contains afferent (sensory) fibers that carry impulses from sensory receptors to the CNS, and efferent (motor) fibers that carry impulses to muscles and glands.

What is the function of the spinal ganglion or dorsal root ganglion?

The spinal ganglion or dorsal root ganglion is a thickening where the cell bodies of sensory neurons are located, receiving and transmitting sensory information to the CNS.

What is the significance of the myelin sheath in nerve fibers?

The myelin sheath, formed by Schwann cells, encloses nerve fibers and increases the conduction speed of nerve impulses by allowing for saltatory conduction at the nodes of Ranvier.

How do nerve cells transmit signals to each other?

Nerve cells transmit signals through synapses. When an action potential reaches the terminal button of an axon, it triggers the release of neurotransmitters into the synaptic cleft, which then bind to receptors on the post-synaptic cell, converting the signal back into an electrical impulse.

What are the different types of skin receptors mentioned in the script?

The script mentions Meissner's corpuscles, Merkel cells, and Ruffini corpuscles as types of skin receptors that respond to different types of mechanical stimuli.

How does a reflex arc work in the spinal cord?

A reflex arc is a neural pathway that allows for a rapid response to a stimulus. Sensory neurons transmit impulses to interneurons in the spinal cord, which then activate motor neurons to cause a response, such as muscle contraction.

What is the difference between white and gray matter in the spinal cord?

White matter in the spinal cord consists of nerve fibers that transmit information, while gray matter contains the cell bodies of neurons where processing of information occurs.

Outlines

00:00

🧠 Central and Peripheral Nervous Systems Overview

This paragraph introduces the human nervous system, emphasizing its complexity and function in processing environmental stimuli. It distinguishes between the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which extends throughout the body. The CNS is well protected within the skull and spinal column, while the PNS is depicted in yellow in the animation. The paragraph also explains the structure of the spinal cord, including the vertebrae, spinal canal, and the protective membranes known as the dura mater and arachnoid mater. Additionally, it describes the function of spinal nerves, which are part of the PNS and connect to the spinal cord, and differentiates between afferent (sensory) and efferent (motor) nerve fibers.

05:00

🌱 Nerve Cell Structure and Synaptic Transmission

The second paragraph delves into the structure of nerve cells, also known as neurons, which are the fundamental units of the nervous system. It describes the components of a neuron, including the cell body, nucleus, dendrites, axon, and terminal buttons. The paragraph explains the role of dendrites in receiving stimuli and the axon in conducting electrical impulses. It also discusses the myelin sheath, which is formed by Schwann cells and increases the conduction speed of impulses through a structure known as nodes of Ranvier. The process of synaptic transmission is highlighted, detailing how neurotransmitters are released from vesicles in the terminal buttons and interact with receptors on the post-synaptic cell membrane to continue the nerve signal. The paragraph also touches on the variety of dendritic spines and their role in post-synaptic signal reception.

10:02

🔁 Sensory Processing and Reflexes in the Spinal Cord

The final paragraph focuses on the sensory processing within the spinal cord and the concept of reflexes. It describes how sensory impulses are transmitted from receptors in the skin and other organs to the CNS via sensory neurons. The cell bodies of these sensory neurons are located in the spinal ganglion, which is why the corresponding part of the spinal nerve is thicker. The paragraph explains the types of sensory receptors found in the skin, such as Meissner's corpuscles, Merkel cells, and Ruffini corpuscles, and their respective roles in responding to mechanical stimuli. It also discusses the direct processing of sensory information in the spinal cord, leading to reflex actions such as muscle contraction or relaxation in response to stimuli like a burn, without the need for brain intervention.

Keywords

💡Nervous System

The nervous system is a complex network of nerve cells, or neurons, responsible for processing stimuli from the environment and coordinating responses. In the video, it is the central theme, with a focus on the human nervous system, which is divided into the central and peripheral nervous systems. The central nervous system includes the brain and spinal cord, while the peripheral nervous system extends throughout the body.

💡Central Nervous System (CNS)

The CNS is composed of the brain and spinal cord, which are the control centers of the body. It is mentioned in the script as being well protected by the skull and spinal column, highlighting its importance and vulnerability. The CNS processes information received from the peripheral nervous system and initiates appropriate responses.

💡Peripheral Nervous System (PNS)

The PNS consists of nerves that run throughout the body, connecting the CNS to the rest of the body, including the limbs and organs. In the script, it is depicted in yellow and is responsible for transmitting sensory information to the CNS and motor commands from the CNS to the muscles and glands.

💡Spinal Cord

The spinal cord is a part of the CNS, which is housed within the spinal column and is responsible for transmitting information between the brain and the rest of the body. The script describes it as being enclosed in three membranes and being connected to the peripheral nervous system via spinal nerves.

💡Nerve Cells

Nerve cells, or neurons, are the fundamental units of the nervous system. They are composed of a cell body, dendrites, and an axon. The script explains that neurons process stimuli and transmit electrical impulses, which is central to the function of the nervous system.

💡Axon

An axon is a long, slender projection of a nerve cell that conducts electrical impulses away from the neuron's cell body. In the script, axons are described as originating from the cell body and having terminal buttons at their ends, which are part of the synapse and crucial for signal transmission.

💡Synapse

A synapse is the junction between two nerve cells where information is passed from one cell to another. The script describes the process of exocytosis at the synaptic terminal, where neurotransmitters are released and received by receptors on the post-synaptic cell membrane, converting the signal back into an electrical impulse.

💡Neurotransmitters

Neurotransmitters are chemical messengers that transmit signals across a synapse. The script mentions them as being contained in vesicles within the terminal buttons, and their release is triggered by the influx of calcium ions, which is essential for the process of signal transmission between neurons.

💡Dendrites

Dendrites are the branching extensions of a neuron that receive signals from other neurons. The script explains that dendrites are mainly used to receive stimuli and are integral to the process of signal integration within the nervous system.

💡Nodes of Ranvier

Nodes of Ranvier are the gaps in the myelin sheath along an axon, which allow for the rapid transmission of electrical impulses. The script describes how Schwann cells can increase the conduction speed of an impulse by forming multiple layers around the axon, creating these nodes.

💡Reflex

A reflex is an involuntary, nearly instantaneous response to a stimulus. The script provides the example of a reflex action that occurs when we burn ourselves, where sensory neurons transmit impulses to interneurons, which then cause motor neurons to contract muscles, illustrating the rapid and automatic nature of reflexes.

💡Sensory Neurons

Sensory neurons are specialized nerve cells that detect changes in the environment and transmit this information to the CNS. The script describes how sensory neurons have receptors that, when stimulated, convert mechanical pressure into electrical impulses that are then transmitted to the CNS.

💡Motor Neurons

Motor neurons are responsible for transmitting signals from the CNS to the muscles, causing them to contract or relax. In the script, motor neurons are mentioned in the context of reflexes, where they are activated by interneurons to produce a rapid muscle response.

Highlights

The human nervous system is a complex system made up of countless nerve cells that process stimuli from the environment.

A distinction is made between the Central and peripheral nervous systems, with the peripheral nervous system running through the entire body.

The brain and spinal cord are part of the central nervous system, well protected by the skull and spinal column.

The spinal cord is enclosed in three membranes, including the outer membrane called dura mater.

Spinal nerves of the peripheral nervous system lead into the spinal cord, divided into afferent and efferent fibers.

Afferent nerve fibers conduct impulses from sensory receptors to the central nervous system.

Efferent nerve fibers carry impulses to affect organs, mainly muscles and glands.

The spinal ganglion or dorsal root ganglion is a thickening where blood vessels and many nerve fibers are part of a spinal nerve.

Fascicle nerve fibers are enclosed by a connective tissue layer, with Schwann cells located underneath.

Schwann cells can increase the conduction speed of an impulse by forming nodes of Ranvier.

Nerve cells consist of a nerve fiber, cell body, nucleus, dendrites, and terminal buttons.

Terminal buttons possess calcium channels that open and close, allowing neurotransmitters to be released via exocytosis.

Neurotransmitters are absorbed by receptors on the post-synaptic cell membrane, converting them back into electrical impulses.

Dendrites have spines with post-synapses that can receive signals from terminal buttons.

Terminal buttons can form synapses with other axons or terminal buttons, facilitating nerve impulse transmission.

Sensory neurons' cell bodies are located in the spinal ganglion, making that part of the spinal nerve thicker.

Neurons in the dorsal root ganglion are pseudo unipolar neurons with axons divided into two branches.

Unmyelinated nerve fibers lack a myelin sheath, meaning there is no increase in conduction speed.

Sensory receptors on fingertips convert mechanical stimuli into electrical impulses transmitted to the brain.

Different types of skin receptors, such as Meissner's corpuscles, Merkel cells, and Ruffini corpuscles, respond to various stimuli.

Action potentials generated by skin receptors are transmitted to the brain via nerve fibers and the spinal cord.

The spinal cord can process impulses directly through reflexes, such as when we burn ourselves.

Transcripts

[Music]

in this animation we want to explain the

human nervous system with the help of

incredible never-before seen

images the body's nervous system is a

complex system made up of countless

nerve cells that serve among other

things to process stimuli from the

environment a distinction is generally

made between the Central and peripheral

nerve nervous system the peripheral

nervous system runs through the entire

body and is shown here in

[Music]

yellow the brain and spinal cord are

part of the central nervous

[Music]

system they are well protected by the

skull and spinal

column

our spinal column consists of individual

vertebrae that have a spinal canal

containing fatty and connective tissue

and the spinal cord like the brain the

spinal cord is enclosed in three

membranes the outer membrane of the

spinal cord is called dura moer the

arachnoid modder is located directly

under the dura modder this arachnoid

modder is connected to the P Mo via

arachnoid

tcul

[Music]

the spinal nerves of the peripheral

nervous system lead into the spinal cord

whereby the spinal nerve is divided into

afferent and ephant fibers the afferent

nerve fibers conduct nerve impulses from

the sensory receptors to the central

nervous system while ENT nerve fibers

carries impulses to affect our organs

mainly muscles and glands we will take a

close closer look at the thickening that

we call spinal gangion or dorsal root

gangion in a

[Music]

moment blood vessels and many nerve

fibers are part of a spinal nerve

several nerve fibers form a nerve

[Music]

faasle nerve fibers are enclosed by a

connective tissue layer of endorian

Schwan cells are located under this

protective layer if these cells are

wrapped around the axon several times

they are able to increase the conduction

speed of an Impulse the increase in

conduction speed is achieved by regular

interruptions which are known as nodes

of

ronier the cell uses an axon to conduct

electrical

impulses

let us first take a look at the basic

structure of a nerve cell nerve cells

consist of the nerve fiber mentioned

earlier which originates from a cell

body inside we see the glowing cell

nucleus dendrites mainly used to receive

stimuli also originate from the cell

[Music]

body at the end of an axon are terminal

buttons

[Music]

these small knobs form the first part of

a synapse and are therefore called press

synaptic

terminals terminal buttons possess

calcium channels that can open and

close these calcium channels open via an

electrical

impulse as soon as the action potential

reaches the terminal button the calcium

channels open and allow calcium ions to

flow

in

there are vesicles in the terminal

button these vesicles contain

neurotransmitters which are shown here

as red spheres there are approximately

200 to 500 such vesicles in the synaptic

terminal

buttons the calcium ions enable these

vesicles to fuse with the outer layer

that is the membrane of the

cell

[Music]

the fusion of the vesicle with the

membrane allows the neurotransmitters to

be transported out of the cell this

process is known as

exocytosis the neurotransmitters are

absorbed by receptors located on the

post synaptic cell membrane which

convert the neurotransmitters back into

an electrical impulse with the help of

such a chemical synapse a nerve cell can

transmit its signal to an another nerve

[Music]

[Applause]

[Music]

cell for this purpose the dendrites have

spines which possess the post synapses

mentioned before spines can take many

forms including stubby and

[Music]

[Applause]

thin

[Music]

terminal buttons can not only transmit

impulses via the spines of dendrites

they can also transmit their action

potential directly to the cell it is

also possible for a terminal button to

form a synapse with another axon or

terminal button nerve cells can and must

also be able to transmit impulses to

other cells such as our muscle cells so

that we can

move but now let's get back to the

spinal cord and nerves the impulses are

transmitted via the nerve fibers on one

side impulses come from the spinal cord

on the other side they are transmitted

to the spinal cord the cell bodies of

the sensory neurons are located in the

spinal gangion that is why this part of

a spinal nerve is thicker than the other

part the neurons in the dorsal root

gangion are pseudo unipolar neurons in

which the Axon is divided into two

branches One Branch goes to the

periphery for example to the skin and

the other to the central nervous

system impulses are transmitted from the

skin to the central nervous system via

the

axon depending on the function neurons

can also have unmyelinated nerve fibers

in that case non-m milina Schwan cells

and sheath the axon that means that

there is no increase in conduction

[Music]

speed let's take a look at the process

with the help of a highly simplified

image on the fingertips in particular we

have numerous receptors at the ends of

sensory nerve fibers if the receptors of

a sensory neuron receive a mechanical

stimulus this stimulus is converted into

an electrical impulse and transmitted

via the a on to another neuron in the

spinal

cord the neuron in the spinal cord

transmits the action potential to the

brain where another neuron finally

transmits the impulse to the somato

sensory cortex the impulse is then

[Music]

processed as already mentioned there are

numerous receptors in the skin some

receptors are are located in the upper

layer of the skin the epidermis which is

made up of dead and living

keratinocytes mner cor pusles and Merkel

cells are found here other receptors are

located in deeper layers of the skin

such as rufini cor pusles which are

found in the

dermis there are many other receptors

but only these three will be briefly

described here let's start with the

meisner's cor

pusle as soon as pressure is applied to

the er's core pusle for example by

pressing on the skin an action potential

is triggered this action potential only

occurs when there is a change in

pressure meisner's cor pusles are

therefore rapidly adapting mechano

receptors Merkel cells on the other hand

belong to the slowly adapting mechano

receptors as they trigger an action

potential in response to both Dynamic

and static

stimuli

rufini cor pusles trigger an action

potential when the tissue is stretched

rufini cor pusles also belong to slowly

adapting mechano receptors of the

skin let's take another look at the

spinal cord and the spinal

[Music]

nerves the axons of the sensory nerves

end at nerve cells in the spinal cord

nerve fibers which can be seen here as

thin threads extending into the brain

originate from the cell bodies of these

nerve

cells the nerve fibers are referred to

as white and the cell bodies as gray

matter when The receptors of the skin or

organs generate an action potential they

transmit this action potential via the

nerve fibers to the gray matter after

which the action potential is

transmitted to the brain via the white

matter

[Music]

from above we can see the

butterfly-shaped structure of the gray

[Music]

matter however impulses can also be

processed directly in the spinal cord

the sensory fibers transmit impulses

directly or indirectly to motor nerve

fibers which can then contract or relax

a muscle this is called

[Music]

reflex such a reflex occurs when we burn

ourselves receptors then transmit

impulses via Sensory neurons to

interneurons which then cause motor

neurons to contract

[Music]

muscles

[Music]