Nervous System

Knowledge

We need to cover Functions of parts of the brain Divisions of the NS and their interrelationships

Autonomic and somatic, sympathetic and parasympathetic

Neurons Transmission of nerve impulse Components of synapse Impulse transmission across synapse

What makes us who we are?

An Interesting Question:

Nature vs. Nurture Nature refers to the

role that “genetics” plays in the development of a person’s behavior or personality traits

Nurture refers to the role that the “environment” plays in the development of a person’s behavior or personality traits

Why does this question have an impact on our

lives? What determines your likes, dislikes, and personality characteristics?

How much of an impact does he environment have on your genetic information?

http://ngm.nationalgeographic.com/2012/01/twins/miller-text

The nature versus nurture question refers to the interactive role that heredity (nature) and environment (nurture) play in human behavior. Although no contemporary psychologist would take either a pure nature or a pure nurture view of human behavior, the extent to which many traits are influenced by genetics and environment is still debated. The related fields of behavior genetics and evolutionary psychology help psychologists explore the influence of heredity on human behavior.

Complete Structures

Structures and Functions of the Brain.

Medulla Oblongata – base of the brain, top of the spinal cord. Brain stem. Reflexive, homeostatic actions. Non-skeletal muscles. Heart rate, breathing rate, swallowing, vomiting.

Cerebrum – divided into R and L and connected by Corpus Callosum. Thinking part, interprets and integrates sensory input.

Thalamus – sorting center or switchboard, impulses destined for the cerebrum (cerebral cortex) are directed by the thalamus to their correct location.

Cerebellum - coordinates movement/balance, located at the top of the spinal cord.

continued

Hypothalamus (not directly associated with thalamus) – lower portion of mid brain. Checks blood conditions and produces chemicals to help maintain homeostasis. Works with pituitary gland.

Pituitary Gland – attached to the hypothalamus. It is involved in production, storage and secretion of hormones. Hormones are chemical messengers (transmitted in blood) which allow different parts of the body to communicate.

Corpus Callosum – the nerve bundles which connect the two hemispheres (sides) of the Cerebrum.

Meninges – 3 layered membrane structure which helps protect the brain.

http://www.nursingassistantcentral.com/blog/2008/100-fascinating-facts-you-never-knew-about-the-human-brain/

Cerebrum: 4 lobes

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Structures

Hemispheric Specialization

The two hemispheres of the cerebral cortex are linked by the corpus callosum, through which they communicate and coordinate. Nevertheless, they appear to have some separate functions. The right hemisphere of the cortex excels at nonverbal and spatial tasks, whereas the left hemisphere is usually more dominant in verbal tasks such as speaking and writing. The right hemisphere controls the left side of the body, and the left hemisphere controls the right side.

PET scans Positron Emission Tomography

Comparisons

Cerebellum Divisions

Spinal Cord

The spinal cord is a complex cable of nerves that connects the brain to most of the rest of the body. It is made up of bundles of long nerve fibers and has two basic functions: to permit some reflex movements and to carry messages to and from the brain.

Control of the body systems from the CNS follows a very ordered sequence. The way we were created puts priority of function at the top, with lesser important functions at the bottom. Why do you think this is?

Neurons: Functional Unit of our Nervous

System

Structure and Function of Neuron

The neuron is the main communication structure of the body, it consists of:

Dendrite (receiving), cell body (summation of impluse), axon (conduct impulse), axoplasm and axomembrane. As well as schwann’s Cells (make myelin), nodes of Ranvier (gaps in myelin), myelin sheath (speeds up transmission)

Be able to label and give a function of these basic parts.

Summary of a

Afferent or Sensory Neuron Notes

In the nervous system, afferent neurons (otherwise known as sensory neurons), carry nerve impulses from receptors or sense organs towards the central nervous system.

A touch or painful stimulus, for example, creates a sensation in the brain only after information about the stimulus travels there via afferent nerve pathways.

Afferent neurons have a single long dendrite and a short axon. The dendrite is structurally and functionally similar to an axon, and is myelinated;

Efferent or Motor Neuron Notes.

In the nervous system, efferent nerves – also known as motor neurons – carry nerve impulses away from the central nervous system to effectors such as muscles or glands. The opposite activity of direction or flow is afferent.

The motor nerves are efferent nerves involved in muscular control. The cell body of the efferent neuron is connected to a single, long axon and several shorter dendrites projecting out of the cell body itself

Nervous System Divisions

Nervous System Divisions

Central Nervous System: CNS made up of the spinal cord and brain.

Peripheral Nervous System: PNS made up of the nerves and ganglia (groups of cell bodies) that are found outside of the CNS. Recall, sensory neurons transmit impulses from the PNS to the CNS and motor neurons transmit impulses from the CNS to the PNS.

Peripheral nerves that communicate directly with the brain are called cranial nerves (12 pairs - connect sensory receptors in nose, eyes, ears, tongue, etc.). Peripheral nerves that communicate with the brain via the spinal cord are called spinal nerves (31 pairs - muscles of the body and various glands and organs).

Peripheral Divisions

The PNS is broken down into two other divisions. These divisions are the somatic nervous system and autonomic nervous system.

The autonomic nervous system (ANS) is further divided into sympathetic and parasympathetic branches.

Somatic Vs Autonomic

The somatic nervous system describes peripheral nerves that receive and send signals to skeletal muscle, skin, and tendons. Sensory receptors in skin, muscle and tendons send information to the CNS about body position and environmental conditions. The CNS relays signals to motor neurons that control the contraction of skeletal muscle and the movement of the body. The somatic nerves control voluntary movements of the body such as walking, jumping, writing, typing, etc. Somatic nerves also facilitate reflex actions that involve skeletal muscles as the effector, such as when you touch something sharp or hot.

Continued

The autonomic nervous system controls involuntary responses to stimuli by the body. Autonomic nerves serve cardiac muscle, smooth muscle, glands, and all of the internal organs. The ANS acts on these various effectors to maintain homeostasis within the body.

ANS is further divided into parasympathetic branch and sympathetic branch

Sympathetic and Parasympathetic

The sympathetic branch of the ANS prepares the body for "fight or flight". This involves several involuntary responses to a stressful situation such as increases in heart rate (effector is cardiac muscle) and respiratory rate, dilation of the pupils (effector is smooth muscle), shunting of blood away from the digestive organs to make more blood available to muscles (effector is smooth muscle of arterioles), and the release of hormones such as adrenalin/epinephrine (effector is adrenal gland).

The parasympathetic branch of the ANS acts to normalize conditions in the body and return the body to a relaxed state. Parasympathetic nerves also cause involuntary responses that increase digestive function, decrease heart rate and respiration, and constrict the pupils.

Summary

Notes on Effectors and contractile proteins:

Effectors are muscles or glands that receive input from the nervous system and ‘do something’ with that information. It can be a muscle contraction or a release of hormones.

A contractile protein is a protein (can be muscle or cellular) which has the ability to contract or change shape. This causes movement.

Adrenalin

Adrenalin (also called epinephrine) is produced in the medulla (middle) of the adrenal glands. The adrenal glands are located on the top of each kidney. The sympathetic nervous system stimulates the adrenal gland (an effector) to release the hormone adrenalin or epinephrine into the bloodstream. Adrenalin is a modified amino acid hormone. The target tissue for adrenalin is mainly cardiac and skeletal muscle. Adrenalin increases heart rate and blood pressure providing more oxygen to working muscles. It also increases blood sugar levels providing more energy to cardiac and skeletal muscles

Reflex Arc: Somatic

Reflex Arc

a simple neurologic unit of a sensory neuron that carries a stimulus impulse to the spinal cord, where it connects with a motor neuron that carries the reflex impulse back to an appropriate muscle or gland

BFF Hypothalamus and Pituitary Gland

Explain how hypothalamus and pituitary gland interact as the neuroendocrine control center. Endocrine (refers to hormones released directly

into the blood stream) Hypothalamus is the ‘brain’ in this relationship.

It monitors blood and directs the hypothalamus with respect to the release of chemicals.

Continued

The neuroendocrine control center is able to maintain homeostasis or internal balance in the body with the help of the autonomic nervous system. It receives information about the status of things such as body temperature, water balance, and the levels of many hormones within the blood and acts to keep them constant.

The neuroendocrine control center is composed of the hypothalamus and pituitary gland. The pituitary gland is made up of the anterior pituitary and posterior pituitary (one lies in front of the other). The interaction between the hypothalamus and the two portions of the pituitary are quite different.

Nerve Impulses

The dendrites and axons of a neuron are basically tubes constructed of cell membrane, called axomembrane, that are filled with cytoplasmic fluid called axoplasm. The electrochemical signal or impulse that allows neurons to communicate travels along the axomembrane.

This section describes how a nervous impulse travels along the axomembrane of a dendrite or axon. When the dendrite of a neuron receives sufficient excitatory stimulation, called threshold, an action potential results. This action potential is an "all or none response". If stimulation exceeds the threshold, an impulse will be generated. Sub-threshold stimulation will not elicit an action potential.

The stimulation that initiates an action potential usually will be generated by sensory receptors for sensory neurons and at a synapse for interneurons and motor neurons.

Resting Potential

Resting Potential

A neuron in the resting state is polarized. Its ready to go. There is a potential difference across the axomembrane of -65

millivolts (mV).

This negative reading means the inside of the neuron (axoplasm) is negatively charged compared to the outside of the axomembrane. This potential difference is produced by the action of the sodium-potassium pump.

Sodium-potassium pumps are membrane proteins that actively transport: sodium ions to the outside of the membrane. (+) potassium ions to the inside of the membrane. (-)

Action Potential

The Action Potential: When the dendrite of a neuron receives stimulation exceeding threshold, an action potential is generated in the axomembrane of the neuron and quickly moves along the dendrite to the cell body and axon.

An action potential is produced by the action of gated channel proteins embedded in the axomembrane. There are gated protein channels for both sodium ions and potassium ions. The action potential has three phases; depolarization, repolarization, and a recovery period. Each of these phases is associated with the action of a membrane protein as summarized below.

Depolarization (facilitated diffusion of sodium ions)

Following an above threshold stimulus, sodium gated channel proteins open and sodium ions rush from the outside of the axomembrane to the inside. This changes the polarity across the neuron from -65mV (resting potential) to +40mV. The axoplasm is now positively charged compared to the outside of the neuron.

Repolarization and Recovery

Repolarization (facilitated diffusion of potassium ions)

Following the movement of sodium into the axoplasm, potassium gated channels open and potassium ions rush to the outside of the axomembrane. This makes the outside of the membrane positively charged relative to the inside once again. The potential across the membrane returns from +40mV back to -65mV.

Recovery/Refractory Period (active transport of sodium and potassium ions)

During the recovery period following repolarization the membrane experiences hyperpolarization or refractory period during this time a neuron can not generate an action potential. The sodium-potassium pump is busy re-establishing the resting potential by

pumping sodium ions out and potassium ions back in through the axomembrane. This recovery period also prevents the action potential from moving backwards.

Saltatory Conduction

Myelin sheaths (neuron wraps) are formed by Schwann Cells. Schwann cells form multiple layers of membrane around the neuron and insulate it. In between the areas of myelin sheath, Nodes of Ranvier or bare patches exist. The nerve impulse or action potential will jump form node to node greatly increasing the speed of nerve transmission.

This node to node transmission, called saltatory conduction, can produce transmission speeds of up to 200 meters per second and explains the speed at which we can react to potentially harmful stimuli.

Synapse Structure

A synapse describes the region at which the axon bulb of a neuron is positioned very near the dendrite or cell body of a second neuron.

Neurons communicate with other neurons at the synapse.

A synapse is composed of a presynaptic membrane on the axon bulb of the first neuron and a postsynaptic membrane on the dendrite or cell body of the second neuron. A very small gap, called the synaptic cleft, lies between the presynaptic and postsynaptic membranes.

Neurotransmitters

Molecules called neurotransmitters relay messages across the synaptic cleft between the two neurons.

The communication between neurons is chemical in nature.

Synaptic vesicles, located in the axon bulb, contain neurotransmitters, produced by the neuron, that are released by exocytosis into the synaptic cleft. These neurotransmitters diffuse quickly across the short distance between the presynaptic and postsynaptic membranes.

Neurotransmitters (there are about 25 different ones and probably others yet to be found) can cause excitation or inhibition at the postsynaptic membrane. A single neuron will have many dendrites and many synapses with other neurons.

Generally, many excitatory signals will depolarize the neuron and cause an action potential, while inhibitory signals super polarize the neuron and prevent an impulse being generated. If both excitatory and inhibitory signals are sent to the same neuron, the signals will add together. Many more excitatory signals than inhibitory signals results in an impulse, while similar numbers of both types of signals will have no net effect on the membrane potential. This adding together of signals from many neurons is called synaptic integration.

Excitatory and Inhibitory

A common excitatory neurotransmitter is norepinephrine or adrenalin and a common inhibitory neurotransmitter is acetylcholine.

If sufficient excitation is caused by neurotransmitters, an action potential may be initiated in the postsynaptic membrane and move along the second neuron.

Neurotransmitters are broken down by enzymes (ex. acetylcholinesterase breaks down acetylcholine) or are reabsorbed into the presynaptic bulb to prevent continued stimulation or inhibition. The steps involved in synaptic transmission are outlined below.

Neurotransmitters

Synaptic Transmission: in 6 easy steps!

Step 1: The action potential reaches an axon bulb and causes calcium ion gates to open and calcium ions move into the axon bulb.

Step 2: The rise in calcium ions in the axon bulb causes synaptic vesicles containing neurotransmitter to move towards the presynaptic membrane.

Step 3: Synaptic vesicles merge with the presynaptic membrane and exocytosis of neurotransmitters into the synaptic cleft occurs. Recall that endocytosis requires ATP energy. The axon bulb contains many mitochondria to produce ATP.

Continued

Step 4: Neurotransmitters diffuse across the synaptic cleft (a very short distance) and bind to receptor proteins on the postsynaptic membrane. Excitatory neurotransmitters cause sodium ions to move through receptor proteins depolarizing the membrane. Inhibitory neurotransmitters do not depolarize the postsynaptic membrane.

Step 5: If sufficient excitatory neurotransmitter binds to receptors, an action potential is produced in the postsynaptic membrane and travels along the length of the second neuron.

Step 6: To prevent continuous stimulation or inhibition of the postsynaptic membrane, neurotransmitters are broken down by enzymes or are reabsorbed through the presynaptic membrane by endocytosis (also requires ATP energy).

Digital Sources

http://outreach.mcb.harvard.edu/animations/actionpotential.swf Interactive Video

http://www.youtube.com/watch?v=DJe3_3XsBOg&feature=related Myelinated vs Unmyelinated.

http://www.youtube.com/watch?v=gkQtRec2464&feature=mfu_in_order&list=UL Khan Academy Action Potential

http://www.youtube.com/watch?v=Tbq-KZaXiL4&feature=mfu_in_order&list=UL Khan Academy: Synapse

http://www.youtube.com/watch?v=90cj4NX87Yk Synapse and AP