Nervous system

Hormones

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peripheral nervous system (PNS)

Consists of nerves that carry sensory messages to the CNS and motor commands from the CNS to the muscles and glands Lies outside the CNS and is composed of nerves and ganglia.

Central Nervous System (CNS)

Consists of the brain and spinal cord, which are located in the midline of the body

Motor neuron

Efferent neuron, carries nerve impulse from the central nervous system (Exiting the CNS) and heads towards an effector (organ/gland) Relays messages from brain or spinal cord to the muscles and organs Short dendrites, long axon

motor end plates

Found only on motor neurons The ending of a motor nerve found in close proximity to effectors (muscles and organs/glands) From here the impulse is chemically transported to the effectors causing an event to take place

Peripheral divisions

Somatic system: - contains nerves that control skeletal muscles, joints, and skin. They receive info from external stimuli (via sensory neurons) and send out nerve impulses to help us appropriately respond (via motor neurons) -Requires thought -some actions in the somatic system are due to Reflexes, which happens quickly without our thinking Autonomic system: -contains nerves that control the cardiac and smooth muscles of the internal organs and the glands. -Automatic, usually without the need for conscious thought -divided into the sympathetic (excitatory)- State of excitation And the Parasympathetic (Normal)- state of relaxation

Differences between sympathetic and parasympathetic

Sympathetic: -fight or flight -Accelerates heart beat, dilates the bronchi, inhibits the digestive tract, activates the adrenal medulla to secrete the hormones epinephrine and norepinephrine -Neurotransmitter is Noradrenalin (Norepinephrine) (excitatory manner) - Short preganglionic fiber long postganglionic fibre -Ganglion near spinal cord - Nerve arise from middle of spinal cord Parasympathetic: - normal activity - neurotransmitter is acetylcholine (normal manner) -long preganglionic fibre short post ganglionic fiber -ganglion near organ - nerve arises from cranium and bottom of spinal cord -promotes digestion of food, causes pupils of eye to contract, slows heart rate

How is the CNS protected

The brain and spine are well protected. Bones including the skull and vertebrae primarily protect the CNS from trauma. The brain and spine are also wrapped in three layers of protective membranes, which form the meninges, in between these layers cerebrospinal-spinal fluid is present to further fusion the CNS.

axon terminals

branches at the end of the axon Each terminal ends with a small swelling (axon bulb) which houses many synaptic vesicles containing neurotransmitter chemicals

Sensory Neurons

Afferent neuron: carrying a nerve impulse from a central organ or receptor, having the impulse arrive at the CNS Relays messages from receptors to the brain or spinal cord Long dendrite, long or short axon

Thalamus

*the "gate keeper" -Above the hypothalamus -channels and prioritized in-coming sensory info (visual, auditory, somatosensory) to the appropriate places of the cerebrum and prevents sensory over load

Similarities between sympathetic and parasympathetic divisions

- functions automatically (involuntarily) -serve all organs - utilize two motor neurons that synapse at a ganglion . The first neutron has a cell body in the CNS, and it's axon is called the preganlionic fiber. The second neutron has a cell body within the ganglion, and its axon is termed the post ganglionic fibre

Cerebellum

-Butterfly shaped structure -makes up the rear, lower portion of the brain; dorsal to the pons and medulla oblangata of the brain stem -receives sensory info from the sensory organs and muscles to help the body interpret present body position -Controls: muscle tone, balance and posture

corpus collosum

-Hold the hemispheres of the cerebrum together - conducts impulses from one side of the brain to the other

Cerebrum

-Largest portion of the brain in humans -conscious brain -Controls: conscious thought -perceives sensory information, and initiated movements, also holds memory -outermost layer is referred to as the cerebral cortex. -Contains two hemispheres (Right and left) -last Center to receive sensory input and carry out integration before commanding voluntary motor responses -carries out the higher thought process required for learning and memory and for language and speech

hypothalamus

-Located just superior and dorsal to the pituitary gland, forms the floor of the third ventricle of the brain *for homeostasis -Also part of the subconscious brain - Controls the pituitary gland (hunger, thirst, sleep, body temp, water balance and BP. The pituitary (master gland) releases the hormones ADH, Oxytocin, TSH, Growth hormone, and more. Maintains homeostasis by controlling the endocrine system, Hypothalamus acts as a direct link between Nervous system and the Endocrine (Hormonal) system

What is a reflex? Why doesn't the brain have to be involved?

-Reflexes are automatic involuntary responses to changes occurring inside or outside of the body. Some involve the brain (such as blinking the eye), while others do not (such as moving your hand away from a hot object) - if the brain were involved it would take too long to respond and serious damage might occur. An impulse would have to travel to the brain, the brain would then have to interpret the message, then the brain would have to send an impulse down to the appropriate effectors to coordinate a response.

What two types of cells make up the nervous system

-neurons (cells that transmit nerve impulses between parts of the nervous system) -Neuroglia/ neurological cells (support and nourish neurons, maintain homeostasis, form myelin, and may aid in signal transmission,)

Medulla Oblangata (POB)

-part of the brain stem -found at the bottom of the brain -pathway between brain and spinal cord - part of the "subconscious brain", contains a number of reflex centres for regulating heartbeat, breathing and vasoconstriction -Also contains reflex centres for vomiting, coughing, sneezing, hiccuping, and swallowing

Transmission across a synapse

-the terminal end of each axon branches off to form many terminal branches (fibers) each of which ends in a swelling called an axon bulb. - Each of these bulbs lies very close to either the dendrite or the cell body of another neuron. This region of close proximity is called a chemical synapse. It is important to note that the two neurons at a synapse do not physically touch, instead they are separated by a tiny gap called the synaptic cleft. -At a synapse, the membrane of the first neuron is called the presynaptic membrane and the membrane of the next neuron is called a post synaptic membrane. -An action potential cannot cross a chemical synapse -Transmission of a nerve impulse across a synaptic cleft is carried out by chemicals called Neurotransmitter substances - As an impulse reaches the end of an axon, not only does Na+ come into the axoplasm, but Ca+ also enters. This Calcium binds with contractile proteins that pull neurotransmitter vesicles out toward the inner surface of the presynaptic membrane.. - These vesicles join with with the presynaptic membrane, resulting in exocytosis of the neurotransmitter so they are released into the synaptic cleft. -The neurotransmitters job is to increase the permeability of the postsynaptic membrane of the next neurons dendrites to Na+ -The Neurotransmitter binds to specific receptor sites on the membrane of a dendrite of the next neuron. If enough transmitter substance is received the Na+ gates will open up and the next neuron will "fire" to continue the impulse through the dendrite and then down the axon of that neuron. - A neurotransmitter only has a short period of time to work once it has been released into the synaptic cleft. Enzymes rapidly break down these neurotransmitters to clear the synapse so the next impulse can be transmitted. (Ex. Monoamine oxidase breaks down Norepinephrine) -There are excitatory and inhibitory neuro transmitters in the body. The stimulation of all the excitatory and all of the inhibitory molecules near the receptors of a dendrite will determine whether or not a dendrite will fire.

Parts of the cerebrum

1. Frontal lobe: conscious though 2. Temporal lobe: hearing and smelling 3. Parietal lobe: temperature, touch, and pain 4. Occipital lobe: vision

Three main types of nerves in the Peripheral Nervous system

1. Sensory nerves: bundles of long dendrites from sensory neurons/receptors 2. Motor Nerves: Bundles of long axons from motor neurons 3. Mixed nerves: contain both long dendrites if sensory neurons and long axons of moror neurons

Myelin sheath

A protective coating formed by a type of neuroglia called Schwann cells, which contain the lipid substance myelin in their plasma membrane. Forms insullating layer around longer axons and dendrites.

Reflex arc

A reflex arc is a nerve pathway that carries out a reflex. 1. Sensory receptor is stimulated and formulates a message by triggering a nerve impulse 2. Sensory (Afferent) neuron carries the message to the CNS (spinal cord), passing the signals onto many interneurons. 3. Some of these many interneurons re-route the incoming nerve impulse directly into a motor (efferent) neuron (synapse with the motor neurons) 4. This motor neuron takes messages away from the CNS carrying it to the appropriate effector (muscle/ organ) 5. The muscle receives the message and contracts. The brain finds out later what had happened. *Reflexes can be controlled

Structures and Functions of a neuron

Cell body: contains the nucleus and cell organelles needed to keep the cell alive. Only a single axon leaves a cell body. Relays an impulse from dendrite to axon Dendrites: exstensions leading towards the cell body that receive signals from other neurons and conduct a nerve impulse towards the cell body. Many dendrites enter a cell body Axons: conducts nerve impulses away from the cell body toward other neurons or effectors.

All or none law

If enough neurotransmitter is received by the postsynaptic fiber, it will fire 100%(all) If not enough substance is received, it will not fire at all (none)

Nodes of Ranvier

Interrupted areas of the myelin sheath due to gaps between one shwann cell and the next. Speeds up transmission of impulse

Interneurons

Lies intirely within the CNS Can receive input from sensory neurons and also other interneurons in the CNS Relays messages from a sensory neuron to a motor neuron Makes up the brain and spinal cord Short dendrite, long or short axon

What is a nerve

Long fibres of many neurons bundled together

Ganglia

Many nerves also have bulges called ganglia. A ganglion is a collection of cell bodies from many neurons. Appears as an enlarged portion of the nerve

How are nerves further categorized

Nerves are further categorized based on where they originate 1. Spinal nerves (humans have 31 pairs, both sensory and motor): arise from the spinal cord. Each spinal nerve forms from two branches that come out of the spine. A dorsal root (sensory) and a ventral root (motor) these roots then merged to form the mixed spinal nerves. 2. Cranial nerves (12 pairs, both sensory, mixed, and motor): Arise from the brain

spinal cord

Part of the CNS Function: -to relay reflex actions -to allow for communication between the brain and the spinal nerves leaving the spine and going out to the peripheral nervous system Structure: -central canal is filled with cerebrospinal fluid -Gray matter is made up of unmyelinated cell bodies. The grey matter has the appearance of an H with two extensions "horns" pointing to the back or dorsal side of the body "dorsal horns", while the other two horns point towards the central surface of the body "ventral horns" - The axons of sensory neurons run into the dorsal horns of the grey matter. Therefore the dorsal (back) part of the cord is specialized for carrying sensory information up to the brain. - The dendrites and cell bodies of motor neurons are located in the ventral horns of the gray matter, and therefore the central cord sends messages from the brain to the effectors of the body. -white matter consists of myelinated long fibres of interneurons. These interneuron bundles connect the spinal cord to the brain. - Interneuron fibres run together in parallel bundles called tracts. Left and right tracts cross over each other prior to entering the brain. Therefore, left side of the brain controls right side of the body and vice versa.

More on neurological cells

Provide physical and metabolic support for neurons 90% of cells in the brain are neurological cells There are 4 different types of neurological cells

Neurotransmission

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Synaptic integration

The summing up of all the excitatory and inhalators signals. If a neuron will received many excitatory signals (either from different synapses or at rapid rate from one synapse), the chances are that the neurons axon will transmit a nerve impulse. On the other hand if the neuron receives both excitatory and inhibitory signals, the summing up of these signals may prohibit it from firing

Mylelinated VS Unmyelibated Fibers

When a nerve fiber is myelinated, it is covered by Shwaan cells, this design allows the nerve impulse to skip from node to node In myelinated axons and dendrites, the impulse can travel up to 200 m/s. In unmyelinated fibers, the maximum speed is 20 m/s. This difference in speed is because the action potential is able to jump over the myelin sheath. Depolarization only occurs at each of the nodes of Ranvier. This jumping is referred to as "saltatory conduction" Invertebrates lack a myelin sheath, therefore they do not exhibit this faster "saltatory conduction"

Nervous system function

controlling, correlating and regulatting the other systems of the body.

Brain

portion of the central nervous system above the spinal cord