4.2 Active Transport in Neurons

Active Transport in Neurons

​Transport Across Membrane

​As the cell membrane is selectively permeable, allowing only tiny, nonpolar materials to cross, there is a need for a passageway for large and polar particles. The cell needs to stock up on these large and polar substances even if their concentration is lower outside. This is where active transport is needed– to move substances against the concentration gradient while utilizing energy.

Multiple Choice

Active transport...

• moves small polar substances without using energy

• moves large nonpolar substances without using energy

• moves large polar substances and uses energy

• moves large nonpolar substances and uses energy

How Small Particles Cross

​When particles are small enough and uncharged, they can either cross through simple or facilitated diffusion. If the particles are small but charged, they can utilize active transport using protein pumps, consuming energy.

​How Large Particles Cross

​When particles are too big or are needed in large quantities, they move in by creating a pouch using the membrane which later pinches off to form a vesicle. This process can happen in moving substances in (endocytosis) or moving them out (exocytosis.)

Endocytosis

​Endocytosis comes in three forms–phagocytosis, pinocytosis, and receptor mediated endocytosis.

Phagocytosis

Phagocytosis is a common way of collecting large food particles or bacteria which will be broken down using enzymes from the lysosomes. Food vacuoles that merge with lysosomes are called phagosome.

Pinocytosis

Pinocytosis (“pino” means “to drink”), otherwise known as fluid endocytosis and bulk-phase pinocytosis is a process of taking in fluids and its solutes into the cell. The pouch created also forms a vesicle.

Receptor–Mediated Endocytosis

As its name suggests, this is specific for substances recognized by a cell-surface receptor. In this process, cells absorb metabolites, hormones, proteins – and in some cases viruses – by the inward budding of the plasma membrane (invagination). This is an important mechanisms on how cells can recognize substances before they are allowed in.

Exocytosis

Exocytosis is the fusion of secretory vesicles with the plasma membrane and results in the discharge of vesicle content into the extracellular space and the incorporation of new proteins and lipids into the plasma membrane. This process can also be initiated by presence of some stimuli.

Multiple Choice

A cell needed to carry inside a bulk of fluids and solute. Which pathway will be used?

• phagocytosis

• pinocytosis

• receptor mediated endocytosis

• exocytosis

Multiple Choice

A bacteria was recognized by a particular white blood cell. Upon recognition, it was attached to proteins on the surface of the membrane and it was brought in. Which pathway was used?

• phagocytosis

• pinocytosis

• receptor mediated endocytosis

• exocytosis

Multiple Choice

After the nucleus transcribed the DNA into RNA, it was converted into proteins and sent out to be secreted on the cell surface. Which pathway is used?

• phagocytosis

• pinocytosis

• receptor mediated endocytosis

• exocytosis

Nervous System

...our window to our internal and external surroundings

Characteristics of Life

A line is drawn between the living and nonliving by characterizing life. These characteristics include having cells, metabolism, the capacity to reproduce and respond to its surroundings.

Responsiveness

Responsiveness is the ability of an organism to adjust to changes in its internal and external environments. An example of responsiveness to external stimuli could include moving toward sources of food and water and away from perceived dangers. Responsiveness can also be internal, as in the case of maintenance of homeostasis.

Key Function

The nervous system collects information or stimuli around, process that information and then respond to it with the help of the PNS and the CNS.

Multiple Choice

What is "stimuli"?

• A major organ in the brain that is a part of the nervous system.

• What your body does to a change or a signal.

• A change or a signal your body receives.

Multiple Choice

The nervous system lets your body know what is going on around you and______________

• changes what is bad for your body.
• maintains the conditions inside your body such as your temperature. 

Multiple Choice

Sensory organs such as eyes and nose are part of the Central Nervous System.

• True

• False

Multiple Choice

Which of the following is not a recipient of 'response' or output from the brain?

• contracting skeletal muscle

• elevated heart beats

• sensitivity of nose to scent

• blinking of the eye

Neuron

The fundamental unit of impulse transmission.

The next few slides present the kinds and parts of a neuron and their corresponding functions. Familiarize yourself with each before you answer the questions.

Cell body

The largest part of a typical neuron is its cell body. The cell body contains the nucleus and much of the cytoplasm. It carries the genetic information, maintains the neuron's structure, and provides energy to drive activities.

Dendrites

Short, branched extensions called dendrites spread out from the cell body. They receive impulses from other neurons and carry impulses to the cell body. 

Axon

The long fiber that carries impulses away from the cell body is the axon. The axon ends in a series of small swellings called axon terminals. A neuron may have dozens of dendrites, but usually only one axon. Axons and dendrites of different neurons form bundles of fibers called nerves. 

Myelin Sheath

The axons of some neurons are insulated by a membrane known as the myelin (my uh lin) sheath. Inside the myelin sheath are the Schwann cells. These cells play crucial roles in the maintenance and regeneration of the motor and sensory neurons of the peripheral nervous system.

Nodes

The myelin sheath around a long axon has many gaps, called nodes (nodes of Ranvier). Impulses move along the axon by jumping from one node to the next. Impulses travel faster along these axons than along axons without myelin. 

Synapse

At the end of the neuron, the impulse reaches an axon terminal. The axon terminal may pass the impulse along to another cell. For example, a motor neuron may pass impulses to a muscle cell. These impulses cause the muscle cell to contract. The point where a neuron transfers an impulse to another cell is called a synapse (sin aps). 

Synapse

At the end of the neuron, the impulse reaches an axon terminal. The axon terminal may pass the impulse along to another cell. For example, a motor neuron may pass impulses to a muscle cell. These impulses cause the muscle cell to contract. The point where a neuron transfers an impulse to another cell is called a synapse (sin aps). 

Kinds of Neurons

• Sensory

• Interneuron

• Motor Neuron

Sensory Neurons

Sensory neurons carry impulses from the sense organs to the spinal cord and brain. 

Interneurons

Interneurons do high-level work. They process information from sensory neurons. Then they send commands to other interneurons or to motor neurons. 

Motor Neurons

Motor neurons carry impulses from the brain and the spinal cord to muscles and glands.

Multiple Choice

When comparing sensory and motor neurons, which of these statements about the morphology of sensory neurons is true?

• Sensory neurons have short dendrites and long axons.

• Sensory neurons have long dendrites and short axons.

• Sensory neurons have long dendrites and long axons.

• Sensory neurons have short dendrites and short axons.

Multiple Choice

The cell shown is most likely an example of

• Sensory Neuron

• Interneuron

• Motor Neuron

Multiple Choice

Which structure primarily functions to receive impulses?

• B

• C

• E

• G

Multiple Choice

Which of the following maintains the neuron structure and provides energy for impulse transmission?

• A

• C

• E

• F

Multiple Choice

Which of the following helps maintain and regenerate motor and sensory neurons?

• B

• C

• E

• G

Multiple Choice

Which of the following allows nerve impulses to move faster?

• A

• B

• D

• F

Multiple Choice

What is the structure B called?

• Axons

• Dendrites

• Schwann cells

• Synapse

Multiple Choice

What is the structure C called?

• Nodes of Ranvier

• Cell Body

• Schwann cells

• Terminals

Multiple Choice

What is the structure D called?

• Synapse

• Myelin Sheath

• Dendrite

• Axon

Multiple Choice

What is the structure E called?

• Myelin Sheath

• Nodes of Ranvier

• Axon

• Neurotransmitter

Multiple Choice

The image shows a Purkinje cell which delivers impulses that causes the heart to beat. Which kind of neuron is it?

• interneuron

• motor neuron

• interneuron