Topic 8

Question 1

What 2 sections is the mammalian nervous system divided into?

Answer 1

Peripheral Nervous System

Central Nervous System

Question 2

What is the central nervous system made up of?

Answer 2

The brain and the spinal cord

Question 3

What is the peripheral nervous system made up of?

Answer 3

• Somatic (voluntary) nervous system
• Autonomic nervous system - made up of 2 antagonistic branches:
  • The sympathetic nervous system
  • The parasympathetic nervous system

Question 4

What does the somatic nervous system control?

Answer 4

Voluntary activity

(e.g. clicking through these flashcards)

Question 5

What does the autonomic nervous system control?

Answer 5

Involuntary activities

e.g. heart rate

Question 6

What do the sympathetic + parasympathetic branches of the autonomic nervous system do?

Answer 6

Anatgonistic branches - act in opposing ways

Allow involuntary responses to be controlled in both direction/ways

e.g. sympathetic increases heart rate, parasympathetic decreases

Question 7

What type of cells make up the mammalian nervous system?

What are the 3 most common types?

Answer 7

Neurones:

Sensory

Relay

Motor

Question 8

What role do sensory neurones play in the nervous system?

Answer 8

Connect sensory receptors to the CNS

Question 9

What role do relay neurones play in the nervous system?

Answer 9

Found in the CNS

Question 10

What role do motor neurones play in the nervous system?

Answer 10

Communicate/pass impulses from the CNS to effectors

Question 11

Label the diagram of a motor neurone including the Schwann cell

Answer 11

Question 12

Draw + label a diagram of a nerve

Answer 12

Question 13

What function do Schwann cells have on a neurone?

Answer 13

Wrap around axon + prodyct a layer of lipid/myelin to insulate it

Prevents flow of ions across membrane so insulates axon

Question 14

Describe how a mammal’s nervous system responds to a stimulus that triggers a reflex response

Answer 14

Sensory neurones carry impulses from receptors to the CNS (made up of the brain + spinal cord)

The CNS (containing relay neurones) processes the information from many sources

It then sends out impulses via motor neurones to effector organs (mainly muscles + glands)

Question 15

Describe the stages of the pupil reflex

Answer 15

The iris contains pairs of antagonisic muscles (radial + circular) that control its size

These are controlled by the autonomic nervous system

In high light intensity, photoreceptors in the retina cause impulses to pass as high freq. along the optic nerve to cells in the brain.

These then send impulses along parasympathetic neurones to the circular muslces of the iris. The muscles contract, reducing the diameter of the pupil + how much light enters

In low light intensity, impules are sent at low freq. to the brain, causing impulses to be send down sympatheic motor neurones to the radial muscles instead. These cause the pupil to dilate.

Question 16

What are the names of the antagonisitc muscles in the iris?

Which cause the pupil to constrict/dilate?

Answer 16

Radial - dilation

Circular - constriction

Question 17

What is resting potential?

Answer 17

The state of nerve fibres when they are not conucting an impulse

Is a dynamic equilibrium that results from an imbalance in the conc of Na⁺ and K⁺ + differences in permeability of the cell membrane to ions

Question 18

What is the potential difference of a neruone/membrane?

Answer 18

The difference in charge across a membrane

Always a comparison - in this case between the cytoplasm + outside of the cell

Question 19

What is the resting potential of a nerve cell usually?

Answer 19

-70mV

Question 20

How can the potential difference of a neurone be measured?

Answer 20

Using a microelectrode connected to a voltmeter

1 end put into the cytoplasm, the other outside the cell

Question 21

Describe how the dynamic equilibrium that causes the resting potential of a neurones is established

Answer 21

The Na⁺/K⁺ pump creates a chemical gradient across the cell by pumping Na⁺ out + K⁺ in

Because there are fewer K⁺ ions outside the cell then inside, the ions diffuse out down the chemical gradient.

This causes the inside of the cell to become more negative (due to loss of + charge)

The negative charge inside the cell prevents the further diffusion of K⁺ + some ions re-enter the cell

Hence the movement of K⁺ in/out of the cell and thus its resting potential is maintained

Na⁺ channel proteins are closed at rest, preventing the ions entering the cell

Question 22

What causes/triggers an action potential?

Answer 22

The depolarisation of a nearby membrane changing the PD to the threshold potential

Question 23

Describe the stages that cause an action potential

Answer 23

• The threshold potential is reached and depolarisation occurs
• Na⁺ gates open, causing Na⁺ to diffuse down the electrochemical gradient into the cell, carrying with it a positive charge.
• As Na⁺ flows into the cell, depolarisation increases, opening more Na⁺ gates (positive feedback). Hence depolarisation is all-or-nothing.
• The polarity of the membrane reverses and reaches +40mV
• Na⁺ gates then close + K⁺ gates open, causing K⁺ to diffuse out of the cell down the electrochemical gradient. The PD of the membrane becomes negative again
• The membrane is hyperpolairsed + K⁺ gates close. K⁺ ions diffuse back into the cell, restoring the resting potential

Question 24

Is the speed of transmission of an AP greater along myelinated or non-myelinated axons?

Why?

Answer 24

Greater along non-myelinated axons

As a result of saltatory conduction

Question 25

What is the flow of ions along a nerve fibre called?

Answer 25

A local circuit

Question 26

What is the refractory period?

Answer 26

Period in which the **AP cannot be generated in the same section of membrane once it has been passed on** Due to movement of **K⁺ back into the cell** Lasts about **5 miliseconds** Ensures **impulse** travels in **one direction** along nerve fibre

Question 27

In nerves without a myelin sheath, what does the speed an impulse travel at depend upon?

Answer 27

Its cross-sectional area Larger = faster

Question 28

Describe saltatory conduction

Answer 28

The 'jumping' of an AP along a myelinated nerve The **only region** of **myelinated nerves** that can be **depolarised** are the **nodes of Ranvier** These means that the **local circuits**/movement of ions **cover a longer distance** than **without myelin** **Depolarisation of one node causes depolarisation of the next** Hence impulse 'jumps' from one node to another

Question 29

Why do mammals have myelinated nerve cells even though impulses travel fastest through non-myelinated nerves with large cross-sectional areas?

Answer 29

Because mammalian nerves only have a **small cross-sectional area** A myelin sheath speeds conduction by **limiting depolarisation to the nodes of Ranvier** This allows **saltatory conduction**

Question 30

Describe how an action potential crosses a synapse

Answer 30

* **AP** arrives in **pre-synaptic membrane**. The membrane **depolarises**, causing **Ca²⁺ channels to open** + Ca²⁺ enter the neurone * **Ca²⁺** cause **synaptic vesicles** containing **neurotransmitter** to **fuse** with **presynatptic membrane** * Neurotransmitter **released** into **synaptic cleft** * **Neurotransmitter binds** with **receptors** on **post-synaptic membrane**, causing **Na⁺ channels to open** + Na⁺ to enter the post-synaptic memrbane * The membrane **depolarises** + initiates the AP again * The **neurotransmitter** can be **taken up** by the **presynaptic membrane** (whole/broken down) or **diffuse away** to be broken down

Question 31

What is acetylcholine? What does it do?

Answer 31

Neurotransmitter Found in all nerves of the **somatic** + **parasympathetic autonomic system**

Question 32

What is the name of the neurotransmitter that breaks down acetylcholine?

Answer 32

Acetylcholin**esterase**

Question 33

What ways/how can the binding of (different) neurotransmitters to (different) receptors on the postsynaptic membrane affect its potential difference?

Answer 33

A receptor with an **excitatory synapse** sends **excitatory postsynaptic potentials** **Opens Na⁺ channels** + brings **PD closer** to **threshold potential** A receptor with an **inhibitory synapse** sends **inhibitory postsynaptic potentials** Postsynaptic **membrane** is **hyperpolarised**, moving **PD away** from **threshold potential**

Question 34

What are the 2 types of photoreceptor cell in the human eye? Where are they found? What do the do/detect?

Answer 34

Found in the retina **Rods** - **Black/white** vision BUT more sensitive to **light intensity** + can work in **dim light** **Cones** - **Colour vision in bright light**. Clustered in the **centre** of the reina at the **back of the eye**

Question 35

Describe how a rod cell detects light (How rod cells function in light conditions)

Answer 35

* **Light energy** is **absorbed** by **rhodopsin** which **splits** into **retinal + opsin** * **Without retinal**, the **opsin binds** to the **membrane** of the **outer segment** of the cell * This causes **cation channels to close**. The **inner segment** continues to **pump Na⁺ out** of the cell + the membrane becomes **hyperpolarised** * This means that **glutamate isn't released** across the synapse. * Glutamate usually inhibits the neurones connecting the rod cells to the neurones in the optic nerve * There is **less inhibition** so an **AP** forms + is **transmitted** to the brain. The information from the optic nerve is processed by the brain in the visual cortex

Question 36

Label the diagram of structure of rods + cones in the retina

Answer 36

Question 37

Describe how rods function in dark conditions

Answer 37

* **No light energy** so **rhodopsin doesn't split** into retinal + opsin * **Lack of opsin** bound to outer segment of cell keeps **cation channels open** * **Na⁺** diffuse through **open cation channels + move down conc. gradient** down cell into inner segment * In the **inner segment**, Na⁺ actively **pumped out** * Membrane only **slightly depolaries**, triggering **release of glutamate** * **Glutamate binds** to **bipolar cells**, **preventing depolarisation** + **inhibiting AP** forming * No signal sent to brain via optic nerve

Question 38

Describe the role of ATP in the hyperpolarisation of rod cells in the retina

Answer 38

ATP supplies **energy** for **active transpor**t needed to **sodium/potassium** (cation) **pump** This **pumps Na⁺ out of the inner segment** + maintains more **negative charge inside the membrane**