Nervous System

Nervous Sytem 

Divisions of the nervous system 

Peripheral nervous system 

Ganglia 

Nerves 

Central Nervous system

Brain 

Spinal chord 

How electrical signals are propagated down a neuron 

And how each neuron communicates with the next 

Introduction 

• The nervous system is very important in helping the homeostasis (balance) within the body 

• A series of sensory receptors work together with the nervous system to provide information about internal and external environmental changes 

Neurons 

• Cell body- is the main processing center of the cell 

• Dendrites- thin branches on the cell body that extends and conducts nerve impulses to the cell body 

• Axon- a singular branch (in most neurons) which conducts impulse away from the body 

Impulse transmission

• Terminal end fibers are found at the axon’s ends and they transmit impulses leaving the neuron across a synapse to the next neuron 

• They are the endings of an axon in a neuron, their job is to send signals to the next neuron through a gap called synapse. When electrical impulses reaches the terminal end fibers, they release neurotransmitters, which will help pass the signal to the next neuron. 

Two major components

• All bodily activities, whether voluntary or involuntary are controlled by the nervous system 

Two major anatomical region are the 

Central nervous system (CNS) - made up of the brain and the spinal chord 

Peripheral nervous system (PNS)- made up of all the nerves that lead into and out of the central nervous system, such as the ganglia and nerves 

• So all the nerves outside the brain and spinal chord 

Automatic and somatic nervous system 

• Automatic is uncontrollable, its involuntary like heart beat. Has parasympathetic (slows down) and sympathetic (speeds up) functions. 

• Somatic nervous system is voluntary aka skeletal muscles like lifting and senses pain, temp etc. 

Nervous system 

• Includes central nervous system brain and spinal chord 

Peripjeral nervous system

• Nerves includes automatic and somatic nervous system 

• Automatic includes sympathetic and parasympathetic (rest and digest) 

• Somatic includes sensory afferent nerve cells that carries signals from the body to the central nervous system aka brain and spinal chord. 

• Motor efferent neurons carry signals to muscles and organs 

The central and peripheral nervous system 

• Neurons are the cells that generates communication between different locations 

• Ex. if a big lands on ur skin your brain is conscious and aware because of the communication the sensation sent along a chain of neurons at the skin when the bug landed. The communication ended in a region of the brain thats dedicated to interpreting sensory information for that location. 

• So basically if a bug lands on your skin, your brain bcomes aware and conscious of it since you felt a sensation. That feeling of sensation communicated to your neuron chains at the skin. Once communicated your brain interpreted the sensory information for the location the bug has landed 

• Glial cells - provides support and structure to the neurons and their activities 

The nervous system divisions of sensation, integration, and response

Afferent- means to or towards the central nervous system. It conveys information from the central nervous system to muscles and glands  (towards muscles and glands) 

Efferent- means away or exiting the central nervous system. It carries motor command information from sensory receptors to the central nervous system. (back tothe cns)

Effector- an organ or muscle that responds and carries and processes sensory information (Aka signal response) 

Central nervous system 

• The central nervous system is composed of two major interconnected organs: 

• - the brain and spinal chord 

The brain contains four major regions: 

1. Cerebrum 

2. Diencephalon 

3. Brainstem 

4. Cerebellum 

Cerebrum 

• The cerebrum can be found above the cerebellum and its iconic wrinkled. Gray globe of the human brain 

• It includes the Cerebral cortex- wrinkled superficial portion 

• Two hemisphere of the cerebral cortex connect because of a nerve fiber bridge which relays information between the hemispheres. 

• That nerve fiber bridge at relays information betwee nthe two hemispheres of the cerebral cortext is called the corpus callosum 

• Broca’s area is an area which is responsible for producing language or controlling movements responsible for speech 

• Wenickle’s area is a major language area, but it doesnt really produce the language unlike the broca’s area, but more contributes to recognizing and understanding spoken or written language. Its kind of like assembling everything instead of producing. Organizing 

Carebrum 

The left and right hemispheres are divided into four different lobes 

1. Occipital lobe (back of the brain) 

2. Temporal lobe mid front next to the occipital lobe 

3. Frontal lobe (front of the brain) 

4. Parietal lobe (in between the frontal and occipital 

Cerebral cortex

• The cerebral cortext contains 

• Lateral sulcus- which separates the temporal lobe from  other regions  like parietal and frontal and is its own landmark 

• Parietal lobe and frontal lobe- superior to the lateral sulcus and are are separated from eachother by the central sulcus 

• Occipital lobe- no obvious anatomical border between it and the surrounding lobes. Its located in the back of the brain with no clear anatomical border. Kind of isolated tbh from nearby lobes 

The corpus callosum 

• The right and left cerebral hemispheres are joined together by a huge bundle of axons which are known as a corpus callosum 

• The corpus callosum unites both the right and left central hemispheres 

Pop media articles are full of references to being “right-brained” or “left brained.” 

• Right brained individuals are described as being more creative and emotional 

• Left brained individuals are described as being more analytical and organized 

• Individuals who are left handed or ambidextrous (use both hands) have a larger corposa callosa. As a group, musicians have a largest corpora callosa. 

Diencephalon

• Its deep beneath the cerebellum 

• It is the connection between the cerebrum and the rest of the nervous system. 

• The rest of the brain, the spinal cord, and the PNS (peripjeral nervous system) all sends information to the cerebrum through the diancephalon/ 

• So basically the brain, spinal chord and the peripheral nervous system sends information to the cerebrum throug the duancephalon. Its kind of like the connection to the cerebrum to send information 

• Except for the olafaction, the sense of small connects directly with the cerebrum. It doesnt go through the diancephalon. 

• Two major regions of the diencephalon 

- Thalamus

- Hypothalamus 

Student study tip

• Any region of the brain with “thalamus” in its name is part of the diancephalon 

Diancephalon Thalamus

• Its a connection of a nuclei that relays (sends back and forth) information in between the cerebral cortex and the periphery/ spinal chord,/ brainstem. 

• Every sensory information, except for the smell senses passes through the thalamus 

• Thalamus is able to edit (adjusts clarity), amplify (keeps important sensory outputs)  or remove (gets rid of weak signals)  sensory information before sending it along to the main cerebrum regions. 

The cerebrum sends information to the thalamus which communicates a motor command 

The thalamus interats with cerebellum and other nuclei in the brainstem -> interacts in basal nuclei -> connection in the thalamus -> relays output to cerebral cortex -> sends information to thalamus 

• The thalamus acts as a central hub, coordinates movement, sensory processing, and communication between different brain regions. 

• So thalamus interacts with the cerebellum and brainstem nuclei, meaning it recieves input related to movement, connection, and sensory signals

• Then it interacts with basal nuclei which helps refine motor control and regulate voluntary movement 

• Connections with the thalamus processes and organizes information 

• It relays output to the cerebral cortex, meaning it sends processed sensory and motor information to consciousness and decisions

• Cerebral cortex sends info back to the thalamus, allowing continuous feedback and signal adjustments

Diancephalon : Hypothalamus 

• Located inferior and slightly anterior to the thalamus 

• Its mainly involved in regulating homeostasis 

• it s the chief regulator of the autonomic nervous system (ANS) aka heart contractions, blood pressure, muscle contractions within the digestive track, temperature, other organ activity 

• Its connected to the pituitary gland 

• Regulates the entire endocrine system 

Sensory information of the hypothalamus 

1. Touching fire. A peripheral neuron receives a painful stimulus (carries signals between the body and the central nervous system) The axon of the peripheral neuron travels within a neve. 

Dont forget, sensory neurons are afferent neurons, meaning towards and towards the cns  aka touch pain temp 

Motor neurons are efferent, so away, meaning it goes from the cns to muscles and glands. 

Interneurons are a connection between the sensory and motor in the pns. 

2. The end of its axon terminates in the spinal chord where it forms a synapse with an interneuron. Meaning the axon of a neuron most likely a sensory neuron ends in the spinal chord and connects to an interneuron through a synapse where it transmits the signal to an interneuron. Interneurons connects sensory and motor neurons through a pathway. 

3. The second neuron fires the signal and tells the cns that a painful stimulus was received from getting burned. The axons then travels within the spinal chord and terminates in the thalamus. The thalamus processes the pain and sends it to the cerebral cortex so the brain can act accordingly   

4. The third neuron communicates the information received from the thalamus to the primary somatosensory cortex. Its axon travels within tracts in the brain. 

5. The primary somatosensory cortex interprets the information 

Explain chat gpt 

• It works alongside the pineal gland 

• The pineal gland is a structure that can be found in the epithalamus 

• The pineal gland  within the hypothalamus helps with the regulation of the sleep and wake cycles 

• The hypothalamus’s pineal gland incorporates light and dark information from the visual system to set the biological clock of sleeping and wakefullness 

• Its like the mind recognizes the light associates it w awake and dark to sleep 

• The pineal gland secretes melatonin, which is a hormone that causes us to feel sleepy, at times dictated by the hypothalamus 

Brainstem 

• Is made up by the midbrain; pons and the medulla oblongata 

Midbrain (its kind of like a root tbh)- is a tiny region in between the thalamus and the pons. 

• Its involved with visual reflexes 

• Pons is a visible bulge on the anterior surface of the brainstem; which controls respiratory functions 

• Medulla oblongata- is the most inferiorly located structure in the brain 

• It contains centers which regulates heart and lung functioning, swallowing, coughing, vomiting and sneezing 

Cerebellim 

• Like the cerebrum, the cerebellum also has an outer cortex of gray matter and inner white matter tracts

• As the name suggests, its the “little brain” 

• It contributes to motor activities (movemenbts controlled by the nervous system 

• Has a role in strategizing and fine-tuningg motor movements initiated by the cerebrum 

• The cerebellum fine tunes and adjusts movements for balance, coordination, and precision 

• Ganglia basal helps and plans refined movement strategies 

Brain systems and functions that bridges regions: Rectic formation 

• A rectic formation starts within the diffuse region of a connected gray matter through the brainstem, diancephalon and the spinal chord. 

• Is an alertness system, filtering sensory input, regulating sleep cycles, and helps with the control of involuntary body movements

• It regulates states of sleep and wakefullness, including general brain activity and attention 

• Reticular activating system (RAS) is a sensory portion which processes the visual, auditory and touch stimuli which can influence alertness 

Cultural connection: sleep hygeiene

• It refers to sleep habits such as regulating the amount of screentime you engage with before bed, or going to bed at consistent times every night, and committing to sleeping for a normal amount of hours every night

• A recent study published in the journal nature, found that college students scored higher on exams when they have slept more 

Brain systems and functions that bridge regions: rapid eye movement sleep 

• A time when the brain is organizing memories which is why we often dream about things ongoing in our daily lives

• CSF (cerebrospinal fluid surrounds the brain/spinal chord) flows differently in the brain during sleep, in slow pulses that act clear to csf and any accumulated toxins from the brain 

• Scientists found that three different frontal lobe regions become activated when the stimulus was a beautiful face, rather than a beautiful work of art 

Peripheral nervous system 

• Is organized into the nerves and the ganglia

• Is the enteric nervous system, which is the system that controls and regulates the gastrointestinal tract 

• Ganglia- a group of neuron cell bodies in the periphery (as either sensory ganglia or autonomic ganglia) outside the pns 

• Sensory ganglia is is afferent and transmits information from the body to the central nervous system (brain and spinal chord) 

• Autonomic ganglia is efferent and controls involuntary functions heart rate etc 

• Ganglia holds the cell bodies of sensory neurons that extends to the central nervous system. 

Peripheral nervous system nerves: 

• Two main classes of nerves in the body are cranial nerves and spinal nerves 

• The peripheral nervous system can be divided in two functional divisions, the somatic (controls voluntary movements and sensory input from the environment) and autonomic divisions (involuntary like digestion) 

Mneumonics

1. Nerves- oh oh oh to touch and feel a girls v?? So heaven??? 

2. Functions- Some say marry money but my brother says big butt matters most 

I Olfactory- smell, have patient identify a scent with their eyes closed

2 optic- visual acuity and field, have patient perform confrontation of a visual field test and a visual acuity test with a snellan chart 

3 Oculomotor- eye movement and pupil size and reactivity and eyelid movement, use penlight to assess patient for perrla 

4 Trochlear- eye movement down + laterally, hold penlight and ask to follow the movement of the penlight. Move down and sideways 

5 Trigeminal- chewing, facial sensation, have pt close eyes take cotton ball and touch face cheeks skin and tell patient to say now when they feel 

6 abducens- lateral eye movement and hold penlight and ask patien to follow movement side to side diagonally 

7 facial- facial expressions, ask patient to frown smile, raise eyebrows, puff cheeks and close eyes tightly 

8 vestibulocochlear- hearing and balance, ask patient to occlude one ear and whispear in another have a patient repeat phrase, ask patient to walk, assess gaut 

9 GLossopharyngeal, gagging and swallowing, ask patient to say ah and have them yawn assess upward movement as soft palate as them to swallow 

Somatic nervous system

• Its responsible for conscious perception and voluntary motor responses 

• But those contractions aren't always “voluntary” like conscious descisions like subconscious muscle control aka breathing (check gpt) 

• Responsible for receiving and processing sensory input from the skin, muscles, tendons, joins, eyes, tongue, nose and ears 

• It also excites the voluntary contractions of skeletal muscles (aka it sends motor contractions from the central motor to the muscles efferent!

Somatic nervous system reflexes 

• Somatic nervous system reflexes dont have contractions between the sensory and motor neurons that dont have the higher brain centers (complex processing conscious control) 

• They also dont include conscious or voluntary aspects of movement bc its a reflex lol 

• A sensory receptor will get stimulated -> an action potential is fired -> it travels of its fiber from dendites -> goes to axons -> then terminates in the spinal chord -> then goes to neurotransmitter -> then goes to motor neuron -> then goes to muscle contractions 

Stimulus → Something happens (e.g., you touch something hot).

Sensory Receptor Activation → Special nerve endings in your skin detect the heat.

Action Potential (Electrical Signal) Starts → The sensory neuron gets excited and fires a signal.

Signal Travels Through the Sensory Neuron → Moves from dendrites → axon toward the spinal cord.

Signal Reaches the Spinal Cord → The sensory neuron releases a neurotransmitter at the synapse.

Motor Neuron Gets Activated → Picks up the signal and sends it to the muscle.

Muscle Contracts → You pull your hand away quickly—without even thinking about it!

Memorize!

Intrinsic vs learned 

• Intristic is a reflex that a person has developed in their fetal period which is shown during childbirth 

• Learned- is developed after birth 

Somatic vs visceral 

• Somatic  (skeleton) reflex is a motor response through a skeletal muscle 

• Visceral- is a motor response that involves smooth or cardiac muscle or gland  (motor response means a reaction to muscle or glands after a stimulus) 

Ipsillateral- begins and ends on the same side of the body- tapping on a patellar tendon of your right knee causes a movement in the right leg like when ur hitting ur knee ur leg moves

Contralateral- it begins and ends on opposite sides of the body 

Ex: Stepping on a sharp object with your right foot causes you to shift your weight to your left   

Autonomic nervous system 

• Is responsible for the involuntary control of the body 

• It carries impulses from the central nervous system to the glands, different smooth muscles, cardiac muscles and various membranes 

• It stimulates organs glands and senses 

• It regulates many of the internal organs through a balance of two aspects or divisions 

Sympathetic nervous system- associated with the preservation of life in emergencies 

Parasympathetic - activity is dominating during times in between emergencies 

Automatic nervous system sympathetic 

• Sympathetic nervous system activation you can imagine the bodys response as it quickly prepares a run from a predator 

• More oxygen needs to be inhaled and delivered to a skeletal muscle 

• Sweating keeps the excess body heat that comes from muscle contraction, just to prevent the body from overheating 

• Blood is shifted away from the digestive system, and its activity is slowed.

• Blood is shifted toward the task of delivering oxygen to the skeletal muscles, like its not a time to eat a snack 

• Pupils dilate and the brain becomes alert to take in more information about potential dangers 

Paraympathetic nervous system 

• The preganglionic neuron in the sympathetic nervous system is usually really long and branched 

• The axons terminate in the ganglia within or near its effect organs 

• The postganglionic neuron in this system us short, its cell body is in a ganglion within or near its effector organ. The target organ is the stomach 

• The synapse occurs in the ganglion. In the parasympathetic nervous system, this ganglion is typically close to the effector organ 

Explain bc what

Parasympathetic nervous system 

There are five main paths of the parasympathetic system:

1. The oculomotor nerve (CN III) invervates muscles that moves the eyeball, which allows you to look in various direction 

2. The facial nerve (CN VII) contains axons of preganglionic neurons that control salivary, mucus and tear glands 

3. The glossopharyngeal nerve (CN IX( also contributes to the production of saliva 

4. The vagus nerve (CNX) innervates organs in the thoracic, abdominal, and pelvic cavities) 

5. The pelvic splanchnic nerves are formed by preganglionic neurons of the sacral portion of the paraympathetic division.