Nervous System: Organisation

What are the functions of the nervous system?

- gather information about an organisms condition & external environment

- process the information

- respond by issuing commands to muscles & glands

What is the function of neurons?

Receive and transmit signals

What is the function of glial cells?

Support & nourish neurons

What does communication take place between in the nervous system?

- sensory receptors

- motor effectors

What are the two main parts that the nervous system are arranged into?

- central nervous system (CNS)

- peripheral nervous system (PNS)

What is the CNS made up of?

- brain

- spinal cord

- processing

What is the PNS made up of?

- sensory nerves and sensory organs

- motor systems

What happens in the PNS?

Neurons carry impulses to/from CNS.

What are the two systems that make up the PNS?

- sensory (afferent) system

- motor (efferent) system

What happens in the sensory system?

sensory neurons carry impulses from receptors to CNS

What happens in the motor system?

motor neurons carry impulses from CNS to effector organs

What senses make up the sensory system and what are the systems called for the senses?

- vision (visual system)

- tase (gustatory system)

- hearing (auditory system)

- touch (tactile system)

- smell (olfactory system)

- balance (vestibular system)

What organs make up the sensory system?

ears, eyes, taste buds, olfactory epithelium

What are sensory receptors connected to in the sensory system?

afferent neurons

What are the two nervous systems that make up the motor system?

- Somatic nervous system (SNS)

- Autonomic nervous system (ANS)

Somatic nervous system (SNS)

- contains voluntary efferent neurons

- skeletal muscles stimulated

- cell bodies in brain stem

- axons synapse at skeletal muscle cells

Autonomic nervous system (ANS)

- involuntary efferent neurons

- visceral muscle, heart muscle, glandular tissue

- sympathetic

- para-sympathetic

What are the 3 nervous systems that make up the autonomic nervous system?

Sympathetic and parasympathetic nervous systems

Enteric nervous system

What happens in the sympathetic nervous system?

Fight or flight.

Response to stress/danger/embarrassment/emotion

How does the heart respond in the sympathetic nervous system?

Increased heart rate, force of contraction and rate of conduction

How do the eyes respond in the sympathetic nervous system?

Pupils dilate to allow more light in

How do the lungs respond in the sympathetic nervous system?

Airway muscles relax to improve oxygen delivery

How does the digestive tract respond in the sympathetic nervous system?

Digestion slows down to divert energy to other parts of the body.

How does the liver respond to the sympathetic nervous system?

Activates energy to be used quickly

How does blood pressure respond to the sympathetic nervous system?

Increases blood pressure

How does sweating respond to the sympathetic nervous system?

Body starts sweating

How do goose bumps respond to the sympathetic nervous system?

Goose bumps activated

How do bronchial passages respond to the sympathetic nervous system?

Bronchial passages widened

How do blood vessels respond to the sympathetic nervous system?

Blood vessels constricted (narrowed)

What happens in the parasympathetic nervous system?

Rest & digest.

Body is relaxed, resting or feeding

How does the heart respond to the parasympathetic nervous system?

Lowers heart rate & blood pressure

How do the muscles respond to the parasympathetic nervous system?

Relaxes muscles in the eyes, lungs & digestive tract

How does digestion respond to the parasympathetic nervous system?

Rate of digestion increased and rate of gastric emptying increased

How does saliva & mucus production respond to the parasympathetic nervous system?

Production of saliva & mucus stimulated

How does urine secretion respond to the parasympathetic nervous system?

Urine secretion increased

How does near vision respond to the parasympathetic nervous system?

Ciliary muscle contracted which improves near vision

How do sphincters respond to the parasympathetic nervous system?

Sphincter muscles in the gastrointestinal system are relaxed

What happens in the enteric nervous system?

- Digestion regulated

- Signals from the sympathetic and parasympathetic nervous system received

- Largely dependent of CNS

- Large numbers of neurons

What are receptors?

Specialised cells that detect changes in the body's environment externally and internally/

What do receptors do?

Convert energy of stimulus into start of a nerve impulse. Called a generator potential.

What are the different types sensory receptors?

- Steady-state receptors

- Changing-state receptors

- Exteroceptive receptors

- Interoceptive receptors

- Proprioceptive receptors

On the skin:

- thermoreceptors

- mechanoreceptors

- nociceptors

Give one example of a mechanoreceptor?

Pacinian corpuscle

they are located deep within the skin

How does a pacinian corpuscle generate an impulse?

1. When pressure is applied to the skin connective tissue is deformed changing the shape of the pacinian corpuscle

2. Stretch-sensitive sodium channels open at the end of the sensory neuron

3. Sodium ions flood in creating a generator potential

4. This generator potential creates an action potential which passes down the neuron

5. The action potential is transmitted to CNS via other neurons

Name 2 photoreceptors?

Rods and cones

Where are rods and cones located?

The retina

What is the retina

The photosensitive layer at the back of the eye

What do cone cells do?

- Allow us to see coloured images.

- Contain the pigment iodopsin

- They are sensitive to high light intensities

What do rod cells do?

- Allow us to see in only black and white as they cannot differentiate colours

- Contain the pigment rhodopsin

- Sensitive to light at low intensity so allows us to see in dim light

What do bipolar cells do?

- Connect photoreceptors to ganglions

- A single bipolar cell connects:

> many rod cells

> single cone cell

Why does one bipolar cell contact to only one cone cell?

Because cone cells show higher visual acuity (the ability to distinguish separate objects)

What do ganglion cells do?

Transmit nerve impulses from bipolar cells to the optic nerve

What does the optic nerve do?

Transmits nerve impulses from retina to the brain

How do rod cells work?

1. Rhodopsin allows vision in poor light

2. Rhodopsin absorbs light and splits into opsin and retinal

3. Opsin causes change in permeability of rod cell to Na+. This initiates a generator potential

4. Rhodopsin may reform in the absence if further light

How do cone cells work?

1. In bright light, iodopsin is broken down and an action potential is generated in the ganglion cell.

2. There are three types of cone cells (green, blue and red).

3. Formed from different forms of iodopsin and different wavelengths of light

4. The colour seen depends on the relative degree of stimulation of different cone cells

What are the three classifications of neurons?

- sensory

- motor

- interneurons

What are sensory neurons and what do they do?

- afferent neurons

- transmit impulse from receptors to CNS

What are motor neurons and what do they do?

- efferent neurons

- transmit impulse from CNS to effectors (muscles and glands)

What are interneurons and what do they do?

- Complex networks in CNS

- Integrate information received

- Relay information

- Direct function of body

What do nerve cells do?

Use electrochemical signals to transmit information

What are the four distinct areas of a neuron cell?

- cell body

- dendrites

- axon

- axon terminal

Properties of the cell body

- AKA 'centron'

- contains cytoplasm

- is nucleated

- contains organelles

Properties of dendrites

- extend from cell body

- short & branched

- receive signals from axons

- contain dendritic spines to increase surface area

Properties of axons

- extend from centron

- 1 neuron contains 1 axon but the axon may branch

- Up to 3 m long

- Carry electrical signal away from centron

Properties of axon terminal

- Connects at synapse to other nerve or effector cells

- Often branched: one neuron can have many synapses

Differences between dendrite and axons

1. Dendrites bring information to the cell body and axons take info away from the cell body

2. Dendrites have rough surface and axons have smooth surface

3. usually multiple dendrites and usually 1 axon

4. Dendrites have ribosomes but axons have no ribosomes

5. Dendrites have no myelin sheath but axons do have a myelin sheath

6. Dendrites branch near to the cell body but axons branch further from the cell body

What are the glial cells in the CNS?

- Astrocytes

- Oligodendrocytes

- Microglia

- Ependymal cells

What are astrocytes?

- star shaped cells that are the most abundant glial cells in the CNS

- they maintain the blood-brain barrier, provide nutrients and regulate neurotransmitter levels

What are oligodendrocytes?

Cells that produce myelin in the CNS

What are microglia?

The immune cells of the CNS, removing debris and pathogens

What are ependymal cells?

Cells that line the ventricles of the brain and spinal cord, producing cerebrospinal fluid

What are the glial cells in the PNS?

Schwann cells, satellite cells

What are Schwann cells

cells that produce myelin in the PNS

What are satellite cells?

Cells that surround neurons in sensory, sympathetic and parasympathetic ganglia

What are the key functions of astrocytes?

- Blood-Brain Barrier (BBB) regulation

- Neurotransmitter regulation

- Synaptic support

- Metabolic support

- Ionic balance

What are the key functions of microglia?

- Immune surveillance

- Phagocytosis

- Synaptic pruning

- Inflammatory response

- Neuromodulation

Which parts of oligodendrocytes are myelinated?

white matter

Which parts of oligodendrocytes are non-myelinated?

grey matter

How are myelinated axons formed in the PNS?

By Schwann cells.

What are nodes of ranvier?

- constrictions in myelin sheath

- 1-2um intervals

What are the three functions of the myelin sheath?

- protection

- insulation

- speeds up impulse transmission

What are nerves?

A bundle of axons located in the PNS that carry info between CNS and the rest of the body.

What are the three types of nerves?

Afferent, efferent and mixed

What are afferent nerves?

carry impulse from sensory receptors to CNS. carry them 1 way

What efferent nerves?

Carry impulse from CNS to effectors. carry them 1 way

What are mixed nerves?

Contain afferent & efferent axons. Carries impulse in 2 ways from CNS and to CNS.

What are cranial nerves?

Have direct connection to the brain for:

- sense organs

- muscles of head, neck & shoulders

- heart

- GI tract

What are spinal nerves?

Carry sensory & motor signals between spinal cord & rest of the body

What is the function of meninges?

Protective coverings of CNS

What are meninges made up of?

dura mater, arachnoid mater, pia mater

What is dura mater?

- "tough mother"

- Dense connective tissue on outermost layer of meninges

- Made up of collagen fibres & blood vessels

- provide protection

- contains cerebrospinal fluid (CSF)

- blood supply to nervous tissue of CNS

What is arachnoid mater?

- "spider-like mother"

- thinner & more delicate

- Lines inside of dura mater

- connected to Pia mater

- crosses sub-arachnoid space

What is Pia mater?

- "tender mother"

- thin, delicate layer on outside of brain & spinal cord

- blood vessel--> feed CNS

- Covers whole of CNS

What is cerebrospinal fluid?

- Formed from blood plasma

- Fills the space surrounding the brain & spinal cord (CNS)

Functions of the CSF

- shock absorber

- brain & spinal cord float in CSF- reduced weight

- maintains homeostasis

- waste product removal