Chapter 3 - Neurons Communicate Quickly Flashcards
What are neurons?
Nerve Cells
- The BASIC STRUCTURAL AND FUNCTIONAL UNITS of the whole nervous system
- HIGHLY SPECIALISED CELLS perfectly designed for rapid communication of MESSAGES in the body.
Summarise the structure of a neuron
Neurons vary in shape and size however, they all consist of a CELL BODY, AXON, DENDRITES, AND NUCLEI (1 each)
What is the cell body? and what can be found there?
also known as the SOMA
- PART of the neuron that CONTAINS THE NUCLEUS
- RESPONSIBLE for CONTROLLING THE FUNCTIONING OF THE CELL
- around the nucleus is cytoplasm containing the organelles that are found in most cells: MITOCHONDRIA, ENDOPLASMIC RETICULUM, RIBOSOMES, AND GOLGI APPARATUS.
What are dendrites?
FAIRLY SHORT EXTENSIONS OF THE CYTOPLASM of the cell body.
often are HIGHLY BRANCHED and they CARRY MESSAGES, or NERVE IMPULSES into the cell body.
What is an Axon?
often a SINGLE LONG EXTENSION OF THE CYTOPLASM
- It usually CARRIES NERVE IMPULSES AWAY FROM THE CELL BODY
- At its end, the axon divides into many small branches. each of these branches terminates at an axon terminal.
- longer than dendrites, axon length varies enormously
eg. brain - only a few millimeters long
eg. axons running down the spinal cord to foot may be a metre or so in length.
What is an Axon terminal?
The end of a branch of the axon.
What is a myelin sheath?
LAYER OF FATTY MATERIAL COVERING MOST AXONS
What are the three important functions of the myelin sheath?
- it as an INSULATOR
- it PROTECTS the AXON FROM DAMAGE
- it SPEEDS UP THE MOVEMENT OF NERVE IMPULSES ALONG THE AXON.
What is a nerve fibre?
the term nerve fibre is used for any long extension of a nerve cell but usually refers to an axon.
myelinated fibres vs. unmyelinated fibres?
myelinated fibers - axon or nerve fibre that have a myelin sheath
unmyelinated fiber - axon or nerve fibre which do not have a myelin sheath
What are SCHWANN CELLS?
special cells that form the myelin sheath which wraps around the axon
What are nodes of Ranvier?
gaps in the myelin sheath forming long intervals
What is a neurilemma?
A sheath surrounding a nerve fibre
- formed by the outermost of the Schwann cell
- around the myelin sheath
this structure helps in the repair of injured fibers
In the brain and spinal cord - white vs grey matter summary
in the brain and spinal cord - myelin sheath is produced by OLIGODENDROCYTES
- the fatty nature of the myelin means that the areas containing myelinated fibres appear white and are called WHITE MATTER.
- The areas made up of cell bodies and unmyelinated fibres are called grey matter due to their grey colour.
What is a synapse?
The junction between the branches of adjacent neurons.
AXON TERMINAL OF ONE NEURON JOINS WITH A DENDRITE/CELL BODY of another
What are neurotransmitters?
A molecule that carries a nerve impulse across the small gap between branches of adjacent nerve cells.
What is a neuromuscular junction?
MOTOR END PLATE
The junction between branches of the motor nerve cell and muscular fibre
- axon meeting a skeletal muscle cell
SIMPLE: how do the nerve impulses be passed from neuron to neuron?
Nerve impulses have to be passed from neuron to neuron —- at a SYNAPSE
NEURONS DO NOT ACTUALLY PHYSICALLY TOUCH AT THE SYNAPSE, WHICH OCCURS BY THE MOVEMENT
- instead, there is a SMALL GAP BETWEEN THEM
- MESSAGES HAVE TO BE CARRIED ACROSS THIS GAP which occurs by the MOVEMENT OF CHEMICALS CALLED NEUROTRANSMITTERS
How can neurons be classified?
Based on their function or structure.
List the functional types of neurons.
- SENSORY
- MOTOR
- INTERNEURONS
What is the FUNCTION of sensory neurons?
AKA - AFFERENT/RECEPTOR neurons
- CARRY MESSAGES from the RECEPTORS IN THE SENSE ORGANS/SKIN to the CENTRAL NERVOUS SYSTEM (BRAIN/SPINAL CORD)
What is the FUNCTION of motor neurons?
AKA - EFFERENT/EFFECTOR neurons
- CARRY MESSAGES FROM THE CENTRAL NERVOUS SYSTEM to the EFFECTORS IN THE muscles or glands
What is the FUNCTION of interneurons?
AKA - ASSOCIATION/CONNECTOR/RELAY neurons
- LOCATED IN THE CENTRAL NERVOUS SYSTEM
- LINK BETWEEN THE SENSORY AND MOTOR NEURONS
Classifying neurons by their structure:
This classification is based on the number of extensions from the cell body
List the structural types of neurons
- MULTIPOLAR NEURON
- BIPOLAR NEURON
- UNIPOLAR NEURON
- PSEUDOUNIPOLAR NEURON
EXPLAIN BIPOLAR neuron
They have ONE AXON AND ONE DENDRITE
- both the dendrite and axon may have many branches at their ends
OCCURS IN THE - EYE, EAR, NOSE
where they take impulses from the receptor cells to other neurons
Explain MULTIPOLAR neuron
Have ONE AXON and MULTIPLE DENDRITES EXTENDING FROM THE CELL BODY
- MOST COMMON:
includes most of the INTERNEURONS in the BRAIN AND SPINAL CORD
MOTOR NEURONS that carry messages to the skeletal muscles
Explain UNIPOLAR neuron
have just ONE EXTENSION - AN AXON
- NOT FOUND IN HUMANS OR VERTEBRAES
FOUND IN INSECTS
Explain PSEUDOUNIPOLAR neuron
HAVE PROPERTIES OF BOTH UNIPOLAR NEURONS AND BIPOLAR NEURONS
- SINGLE AXON FROM THE CELL BODY - which separates into 2 EXTENSIONS
- ONE EXTENSION CONNECTS TO DENDRITES
- the other extension ENDS IN THE AXON TERMINALS
the ARRANGEMENT OG CELL BODY AND AXON = that the CELL BODY LIES TO ONE SIDE OF THE MAIN AXON.
found as
SENSORY NEURON - that carry messages to the spinal cord
NEURON VS. NERVE FIBRE VS. NERVE
NEURON: a nerve cell
NERVE FIBRE: any long extension of the cytoplasm of a nerve cell, although the term usually refers to an axon
NERVE: bundles of nerve fibres held together by connective tissue
Study the diagrams of nerves
- main structure of a neuron
- types of neurons
- neuron vs nerve vs nerve fibre
What is a receptor?
A receptor is a structure that is able to detect a change in the body’s internal or external environment.
- A STRUCTURE THAT DETECTS A STIMULUS
When a receptor is stimulated, the body is able to respond to the change.
Via AUTOMATIC REFLEX, OR other cases the RESPONSE IS MORE COMPLEX.
What is a sense organ?
Receptors grouped into a discrete organ such as the light receptors in the eye or the receptors sensitive to sound vibrations in the ear
Other receptors?
Other than sense organs, other receptors SIMPLE NERVE ENDINGS and may be SPREAD THROUGH PARTS OF THE BODY OR EVEN THE WHOLE BODY
eg. pain, touch etc.
Define Stimulus:
stimuli - plural
Any change, internal or external that causes a response
Changes in the environment- coming from different sources
Changes in the environment come from different sources. Therefore different types of receptors to be able to detect the different types of stimuli. List the different types of Receptors:
- Thermorecptors
- Osmoreceptors
- Chemoreceptors
- Mechanoreceptors
- Nociceptors
others
- stretch receptor
- hair receptor
- fine touch receptor
- balance receptors
What are THERMORECEPTORS?
Receptors able to RESPOND TO HEAT AND COLD
Skin thermoreceptors inform the brain (hypothalamus and cerebrum) of changes in temperature OUTSIDE THE BODY
- in this way we are consciously aware of the temp of our surroundings
Found at NERVE ENDINGS, sensitive to HEAT OR COLD, NOT BOTH.
- DEFINITE HOT SPOTS AND COLD SPOTS
CORE TEMPERATURE is monitored by the RECEPTORS IN THE HYPOTHALAMUS
- detects temp of blood that is flowing through the brain
What are OSMORECEPTORS?
Determines OSMOTIC PRESSURE (DETERMINED BY THE CONCENTRATION OF WATER IN BLOOD PLASMA)
HIGHER CONCENTRATION = HIGHER OSMOTIC PRESSURE
OSMORECEPTORS ARE LOCATED in the HYPOTHALAMUS and are sensitive to even very small changes in osmotic pressure.
They CAN STIMULATE THE HYPOTHALAMUS so that the body’s water content is maintained within very narrow limits.
WHAT ARE CHEMORECEPTORS?
receptors stimulated by particular chemicals.
LOCATED IN NOSE (sensitive to odors), MOUTH (sensitivity to taste).
also INTERNAL chemoreceptors SENSITIVE TO THE COMPOSITION OF BODY FLUIDS.
EG. in certain blood vessels they are sensitive to pH LEVELS of blood, oxygen, CO2, and hydrogen concentrations.
These are INVOLVED IN THE REGULATION OF THE HEARTBEAT AND BREATHING.
What are Touch Receptors? (5)
mechano or pressure receptors
located primarily in the SKIN
NUMBER OF DIFFERENT TYPES EXIST
- FINE TOUCH (MEISSNER’S/TACTILE)
CLOSER TO THE SURFACE AND SENSITIVE TO LIGHT TOUCH
- OCCURS IN GREATER CONCENTRATIONS IN THE LIPS, FINGERTIPS, EYELIDS, EXTERNAL GENITAL ORGANS. - LAMELLAR CORPUSCLES
nerve endings found at the base of the hair follicles
-responds to any light touch that bends the hair - Ruffini endings (pressure and vibration receptor)
- located deeper in the skin and sensitive to pressure and vibrations - Stretch receptors
- Picean corpuscle
- pressure receptor close to the skin surface (just under dermis)
- adapt rapidly (all hair recp) and so after a long time, we are unaware of sensation/pressure eg clothing on skin.
What are pain receptors?
NOCICEPTORS
- STIMULATED BY DAMAGED TO TISSUE
(cut, heavy bump, poor blood flow, excessive stimulation from stimuli - heat/chemicals)
-extremely concentrated in SKIN AND MUCOUS MEMBRANES
- ADAPTS LITTLE OR NOT AT ALL- pain continues as stimulation is present sometimes makes it worse
What is a reflex?
rapid, automatic response to a change in the external/ internal environment
- some involve the unconscious part of the brain
- most are coordinated by spinal cord
What is the property of all reflexes?
- a STIMULUS is required to trigger a reflex - reflex is not spontaneous
- A reflex is INVOLUNTARY - it occurs without any conscious thought
- A reflex is RAPID - only a small number of neurons are involved
- A reflex is STEREOTYPED - it occurs, in the same way, each time it happens
What is a spinal reflex?
reflex carried out by the spinal cord
- impulse may be passed to motor neurons at the same level in the cord, or a few segments up or down the cord before traveling out through a motor neuron.
What is a Reflex arc?
The pathway a nerve impulse follows in travelling from a RECEPTOR TO AN EFFECTOR
in case of spinal reflex = spinal reflex arc
What are the Basic Components of a reflex arc?
- The RECEPTOR reacts to a change in the internal/external environment by INITIATING A NERVE IMPULSE in the SENSORY NEURON
- A SENSORY NEURON carried impulses to the RECEPTOR OF BRAIN/SPINAL CORD
- At LEAST ONE SYNAPSE; the nerve impulse MAY BE DIRECTLY PASSED TO A MOTOR NEURON, OR there may be one/more INTERNEURONS THAT DIRECT THE IMPULSE TO THE CORRECT MOTOR NEURON.
- MOTOR NEURON carries the impulse to nerve fiber to an EFFECTOR
- an effector RECEIVES THE NERVE IMPULSE and CARRIES out the APPROPRIATE RESPONSE.
EFFECTORS = MUSCLES CELLS OR SECRETORY CELLS - Brain is aware once reflex is initiated if not gone to the brain already
another response is done by the autonomic nervous system
Innate vs acquired reflexes
INNATE
- determined genetically
protective reflexes from birth
such as suckling, chewing or following movements with eyes
Acquired
- complex motor pattern learned
- muscular adjustments required to maintain balance
- learnt through constant repetition
- balance while bike riding, catching a ball
What is a nerve impulse?
The message that travels along a nerve fiber.
- Transmitted very quickly, making it possible for the body to respond rapidly to any change in the internal/external environment.
Why is a nerve impulse considered an electrochemical change?
a NERVE IMPULSE is an ELECTROCHEMICAL CHANGE that travels along the nerve fiber.
- A CHANGE IN ELECTRICAL VOLTAGE
- BROUGHT BY THE CHANGE IN CHEMICALS (specifically the concentration of ions inside and outside the cell membrane)
What is the potential difference?
A difference in electrical charge between 2 locations
- can be measured in VOLTAGE in Volts (V) or millivolts (mV)
1000mV = 1V
What is membrane potential?
Differences in the concentration of ions mean there is a potential between the inside and the outside of the cell membrane.
This potential difference is called the membrane potential.
What are leakage channels? vs VOLTAGE GATED CHANNELS
Ions are unable to diffuse through the phospholipid bilayers of the cell membrane directly.
- Instead they move through protein channels.
- leakage channels = open all the time
- voltage-gated channels = only open when a nerve is stimulated
What is the resting membrane potential mainly due and their concentrations?
- k+ (negative inside )
- Na+ (postitive outside)
- Na is 10x higher outside the neuron
- K is 30x higher inside
- higher Cl (-) ions outside
- concentration of large, negatively charged organic ions is higher inside (makes inside negative)
What is the sodium-potassium pump
CARRIER PROTEIN
A mechanism in the membrane of a nerve cell that transports sodium ions out of the cell and potassium ions into the cell by active transport
2 potassium to three sodiums
What is an action potential?
If stimulus to a neuron is sufficient then the signal is passed along the neuron.
- 1 millisecond it is completed and needs 15 millivolts
- rapid opening and closing of gates
- rapid depolarisation and repolarisation of the membrane
List the stages of a nerve transmission
- POLARISATION
- Resting potential
- Action potential
- Repolarisation
- Hyperpolarisation
- REFactory period.
